texts: Electron configuration from vanadium to chromium?

texts:
The electron configurations for vanadium is: $\ce{1s^2 2s^2 2p^2 3s^2 3p^6 3d^3 4s^2}$, and the electron configuration for chromium is: $\ce{1s^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^1}$.

In looking at the electron configurations of two consecutive elements, I noticed that an electron in the $\ce{4s}$ orbital "jumped" to the higher energy $\ce{3d}$ orbital. Why is this so?


texts: Does attachment of phenyl to an alkene increases its reactivity towards electrophilic addition reaction?

texts: According to me phenyl should decrease the reactivity as its electron withdrawing nature destabilises the carbocation.


texts: What happens when oxidizing Ni(OH)2 with a strong base?

texts:
In an aqueous solution, Nickel oxyhydroxide is oxidised with a 1:1 ratio of aqueous Sodium hydroxide. My goal is to produce Nickel oxyhydroxide ($\ce{NiOOH}$).

Strong Base: $\ce{NaOH + H2O \leftrightharpoons Na+ + OH-}$
Add that to some stirred $\ce{Ni(OH)2}$:

$$\ce{ Ni(OH)2 + OH- \leftrightharpoons NiOOH + H2O + e-}$$

This is where things get difficult; wouldn't the spare electron be used by the sodium ions to make $\ce{Na (s)}$?:

$$\ce{ Na+ + e- -> Na (s) }$$

But then, $$\ce{Na(s) + H2O \leftrightharpoons NaOH }$$

That just brings everything back to the beginning.

I guess the real question is: will the initial oxidation of the $\ce{Ni(OH)2}$  happen? If not, how can I force it? I initially thought of just grounding the solution, as odd as that sounds.

Thanks for your help!

P.S. I'm a 12th grade high school student.


texts: How does a carbocation have a positive charge?

texts: When an alkene bonds with an H+ ion, the electron pair from the pi bond goes towards a new dative covalent bond with the hydrogen ion, leaving, on one side of the old double bond, a carbon bonded to an extra hydrogen, and on the other side, a carbocation with a positive charge. If this gave, for example, a tertiary carbocation, I would like to know how this has a positive charge given that it has 3 bonding pairs of electrons around it, which would give it 6 valence electrons and 8 electrons overall. If carbon has 6 protons, how does this give an ion with a positive charge? I understand that it has lost electrons that were previously in the pi bond, but I don't see how it has a positive charge given that it still has more electrons than protons.


texts:
I milled a small amount of the sample ($75\%$ Al, $15\%$ Cu, $10\%$ Ni) mixed with toluene for 5 hours after which I set it on butter paper to dry. Then after 13 minutes I switched on the fan in the room, at which point my powder caught fire.

Could you please explain why my powder would have caught fire?


texts: Why don't labile protons such as -OH and -NH have a characteristic chemical shift?

texts: Is it simply because the H instantly disassociates so it is a proton with zero shielding?


texts: Why are polynuclear carbonyl complexes coloured?

texts:
We know that polynuclear carbonyls are colored and their intensity increases with increase in metal ions. But why does the color arise?

I am aware that this is due to some transition between electronic energy levels; but, what sort of transition takes place?
Is it due to transition between orbitals that are largely localized on the ligands i.e. CO, or is due to transition between orbitals localized on metal frame work?

I have tried gathering some information about the same and I have found something called metal to ligand charge transfer (MLCT) that is responsible for colors in complexes, but I am not sure whether this is applicable in this case or not.


texts: This is a question of JAM 2017. According to the answer key the answer is 4. But I found only the last 3 as aromatic . So which one is the 4th aromatic compound? Please explain


texts: Asking about definitions of word "sugar" in biochemistry

texts: In a lecture about anabolic pathways of sugar, the lecturer was not clear when stating the name of a multiple sugar carrier & it sounded like "dolichol"so is it correct?


texts: What is the formula of potassium ammonium sulfate?

texts:
I tried to get the formula of potassium ammonium sulfate. What I got is $\ce{K(NH4)2SO4}$ but I don't think this the right formula. I searched on the internet and found an answer ($\ce{KNH4SO4}$), but I don't think it is correct.

So what is the correct formula of potassium ammonium sulfate?


texts: Mono-addition of HCl to unsymmetrical dienes?

texts: I completed 3/4 of the answers, by choosing the correct reaction pathways leading to each of the 3 different products. But I don't know how to draw the reactant diene, I really thought what I initially had was correct, should I make a trans reactant or is there something else missing?


texts: Why Does 0.10 M Dihydrogen Phosphate Dissociate Rather than Hydrolyse in a Neutral Solution of Water?

texts:
Dihydrogen Phosphate has a Ka of 6.2x10^-8, yet it seems to form solutions with an acidic pH when it is in water.  Why is that?  Shouldn't it dissociate back to phosphoric acid and form a basic solution, since its Ka is less than 1.0x10^-7?

It seems as though Ka does play a role in determining whether an amphoretic substance will act like a base or acid, since 0.10 M Hydrogen Phosphate has a Ka of 4.8x10^-13 and creates a basic solution.  However, I feel like I am missing another mechanism that determines the behavior of an amphoretic substance in a neutral solution.


texts:
I apologize if this isn't a sufficiently technical question to be posed in this forum.

I'm planning a short story, and unfortunately I've worked in a somewhat sience-y opening. Most of the information I need can be found online, but so far I haven't been able to find any comprehensive information about the properties of some of the less common gases, namely tungsten.

Would pure tungsten gas be visible to the human eye? Does it have any other unique properties that I should know before writing about it?


texts: What would happen if you tried a Williamson Ether Synthesis on something that has both an alcohol and a carboxylic acid? Would both -OH groups be functionalized, where the alcohol would become an ether and the carboxylic acid become an ester?


texts: Does a freezing point of a substance always increase as its boiling point increases?

texts:
I am studying for an introductory to physical sciences test and came upon a chart describing substances found in petroleum and the distillation process.

Each freezing point increases as each boiling point increases.  Each of these properties also increases with the rise in density.

Is this just true for substances in petroleum (methane, ethane, propane, butane, pentane...) or is this consistent throughout all substances?

Update:

(Pure substances)


texts:
We all know that oxidation of secondary alcohols leads to ketones. So, with that logic, in order to form acetone $CH_3-CO-CH_3$ through oxidation, we need a secondary alcohol like isopropyl alcohol. Now there is a problem I am trying to figure out, where I need to identify each reactants + reactions involved.

It is given that acetone is the end product , now with that information I need to traverse backwards/in backward direction and determine A, B and C. First let me mention the reaction procedure:

$A+HI\rightarrow B+KOH\rightarrow C+[O]\rightarrow Acetone$

Now, it is quite clear that C represents isopropyl alcohol (oxidation of secondary alcohols). Now, isopropyl alcohol has OH group in the second carbon atom, and that must have come from KOH. Also, since C (as a product) has 3 carbon atoms, hence B must also have 3 carbon atoms. Now, what is confusing me is this part:

$A+HI\rightarrow B+KOH$

Since, in the reactant side there is I (iodine) group, hence, B (as a product) must have iodine in it. But considering C, there is no iodine (I) group in it, so does it mean that I group was substituted by OH group? Because, normally, i have seen $OH$ group being substituted by I group. Also, I don't think that A will be alcohol (because C already is an alcohol), moreover it is quite apparent that even A must have 3 carbon atoms...or does it not? (I am not sure). Also, considering B, it is sure to have I group on second carbon atom. Is my approach correct? (Please correct me if I am wrong). What according to you should be A and B?


texts: Why does lactose-free milk last so much longer than regular milk?

texts: I buy lactose-free milk. The sell-by date is usually as much as eight weeks from the date of purchase, which is in the neighborhood of twice that of regular milk. This seems puzzling; lactose-free milk, which still has the same mass of sugar, has twice as many sugar molecules as regular milk, since all the lactose molecules have been split in to galactose and glucose. With twice as many sugar molecules per unit volume, one would think lactose-free milk would last half as long as regular milk, not twice as long.


texts: How do I calculate the equilibrium constant of a reaction from two related reactions' constants?

texts:
At a certain temperature the following reactions have the constants shown:

  $$\begin{align}\ce{S(s) + O2(g) &<=> SO2(g)} && K'_\mathrm{c} = 4.2\times 10^{52}\\
\ce{2S(s) + 3 O2(g) &<=> 2 SO3(g)} && K''_\mathrm{c} = 9.8\times 10^{128}\end{align}$$

  Calculate the equilibrium constant $K_\mathrm c$ for the following reaction at that temperature:

  $$\ce{2SO2(g) + O2(g) <=> 2 SO3(g)}$$

I already have the answer (which is given in the back of the textbook): $$K_\mathrm{c}=5.6\times10^{23}$$

But whenever I complete the problem (I've done it thrice) I get $2.3\times10^{76}$.

My process for solving this is as follows. I reverse the first equation and double the coefficients. Since I've done this, I use the inverse of $K'_\mathrm{c}$, $(K_\mathrm{c}')^{-1}$. I then multiply both $K$ values and the result is $2.3\times10^{76}$. Where is my mistake?


texts:
If I wanted to isolate cis-3-hexanol (cis-3-hexen-1-ol;  IUPAC name: (Z)-Hex-3-en-1-ol ) from grass I could start the extraction by dissolving the grass in a solution of ethanol. EtOH is a common solvent for extractions, and dissolving grass in it would leave some remaining solid, as well as a crude solution containing the cis-3-hexanol. Cis-3-hexanol is a liquid at room temperature and is soluble in ethanol but not (only to a small degree) soluble in water.

After filtering out the remaining undissolved solids, I think the next best step would be to boil off the remaining ethanol and water with both of their boils points being lower than cis-3-hexanol's boiling point at around 156.5 degrees C. This would presumably leave a crude solution containing cis-3-hexanol and other organic components extracted from the grass.

What would be the best method to further purify the remaining solution for a higher purity? Please correct me if my thought process is wrong.

Cis-3-hexanol is used in perfumes and the demand for it has increased in industry.


texts:
This question relates to a few earlier questions I have seen on the site (particularly this one about the bond strength of heavier isotopes). Does a bond necessarily have to be shorter to be stronger?

To my understanding, length and strength are definitely correlated, but I don't think it is necessarily a one to one correspondence. The examples I brought up in the comments of ron's answer in the linked question related to data tables that seemed to show no difference in bond length for deuterium substituted bonds despite significant changes in energy. (HCl NIST, DCl, data table)

To expand on my question, if length and strength are always directly related:

How do we explain experimental and theoretical cases where the length doesn't differ with bond energy?
If there is some direct relationship between length and strength, what is that relationship?

For the sake of not being too general, I'm looking for an answer focused on comparing bonds of the form $\ce{A-B}$ and $\ce{A-C}$ (similar to the examples I asked about in the linked question). So for a more specific case related to the linked question, does substituting a protium for a deuterium always make the bond shorter in addition to being stronger?


texts: Charactaristics of Certain Hydroxyl Protecting Groups

texts: I have been reading through Philip J. Kocienski's book Protecting Groups to try to better understand some of the characteristics of hydroxy protecting groups. I am looking to understand the compatibility of silyl ethers, alkyl ethers, alkoxymethyl ethers, tetrahydropyranyl, methylthiomethyl ethers, esters, and carbonates with acidic conditions; however, my book is very vague on this. Which of these classes of protecting groups will be compatible with strongly acidic conditions (specifically, I will need it to remain intact in HBr for an addition reaction). I am just looking to know which categories are best for these conditions so I can narrow my search. So far, based on what I have read, the Troc protecting group would best suit strongly acidic conditions; however, it is highly electron withdrawling, which will likely affect an addition reaction I am looking to perform.


texts: What difference between pi bond and bent bond? Is it possible to replace sigma-pi bond model and use only bent bond instead?

texts:
Between sigma-pi bond and 2 bent bonds, is it actually equiavalence? Or there is specific molecule that require to be bent bonds and cannot exist as pi bond and vice versa? I felt like we actually don't need pi bond model at all if we consider it all to be bent bond
If it not, then how can we consider which chemical result will be bent bond, and which will form pi bond?


texts: Molality of solution having more than one solute?

texts:
So here is my question,

  Question: A water sample contains 9.5% $\mathrm{MgCl_2}$ and 11.7% $\mathrm{NaCl}$ (by weight). Assuming 80% ionization of each salt. Boiling point of water will be ________. ($\mathrm{K_b}$ for water $\mathrm{=0.52}$)

You know, this question isn't that tough to bother anyone (definitely not!). What's all confusing here is the molality of two solutes.

I know that,

$$\Delta \mathrm{T_b=K_b\cdot m}$$

Degree of dissosiation $(\mathrm{\alpha}) = 0.8$

So I know very well that molality of a solution having only one solute is,

$$\mathrm{m=\frac{n\ (no.\ of\ moles\ of\ solute)}{y\ (mass\ of\ solvent\ in\ kg)}}$$

But what about the solution having more than one solute? Do they have any molality (I am sure that there will surely be, because it is there in the question). If yes then what's the method of calculating?

Also if you are solving this, here is the answer to the question (as per my answer key),

  377 K


texts: Formula of the compound based on occupancy of lattice voids

texts:
Atom of element $\ce{B}$ forms HCP lattice and those of the element $\ce{A}$ occupy 2/3rd of tetrahedral voids. What is the formula of the compound formed by the elements $\ce{A}$ and $\ce{B}$?

My doubt is that since the element $\ce{B}$ is in HCP, the number of octahedral and tetrahedral voids will be 6 and 12, respectively, which means that $2/3 \times 12 = 8$ tetrahedral voids occupied by $\ce{A}$.

Since $\ce{B}$ is in HCP lattice, there must be 12 voids, i.e. the ratio will be $8 : 12 \implies  2 : 3$, so $\ce{A2B3}$ must be the answer.

But according to NCERT textbook (example 1.2) the answer is $\ce{A4B3}$.


texts: Meisenheimer complex in Preparation of 2-Naphthol from 2-Naphthalenesulfonic acid

texts:
I'm trying to figure out the addition-elimination mechanism for the preparation of 2-naphthol from 2-naphthalenesulfonic acid. I know that the $\ce{SO3^2-}$ group is functioning as the leaving group, but I don't know how to draw the Meisenheimer complex.

I also can't find anything on the internet about the Meisenheimer complex of naphthalene, I tried to draw it, but this became too hard for me as there were too many resonance structures. Can someone please help?


texts:
There is a reaction given in my book:

$\ce{2FeSO_4 +Heat -> Fe_2O_3 + SO_2 + SO_3}$

I just noticed that on the left $\ce{Fe}$ has valency $2$, while it has $3$ on the right. How can it change valency?

Changing the number of electrons is easy, but this only changes the charge, not the valency. Does this mean that the number of protons changes?


texts: Group Theory and Chemistry for Undergraduate Thesis

texts: I am advising a student on her senior math thesis.  She would like to involve chemistry somehow (her other major).  I know no chemistry.  I have read in several places that representation theory features prominently in some areas of chemistry.  When I try to read anything online I am not sure how much chemistry one needs to assume.  So, if my student is in her senior year of a chemistry major, are there any places where she can start to look for a project in group theory and chemistry?


texts: Converting cyclic compounds to their corresponding aliphatic compounds

texts:
Is there any reaction available to convert cyclic compounds to their corresponding aliphatic compounds?
eg. Converting cyclohexane to n hexane


texts: What (stored-as-solids) acids/liquids can clean corroded copper?

texts:
I'm looking for a liquid that can remove copper corrosion (oxides and basic carbonates - the black and green stuff) off copper piping.
The corrosion will be located on the inside of the pipe, in hard-to-reach areas, so ideally I should be able to just pour the liquid in, leave it for a while, and just flush it out with water. It will be practically impossible to scrub the corroded areas.
Additionally, the piping is brazed or soldered together with an unknown filler metal.
I've read around, and it seems people commonly use acetic acid (vinegar) or hydrochloric acid for this. Is this correct?
However, I'm interested in if any acids (or other liquids) that can be stored as solids can be used for this instead. Mainly because it's easier to store and transfer solids than liquids. (As far as I'm aware, acetic and hydrochloric acid are only readily available in liquid forms)
Some common solid acids that seem to be effective on rust (iron oxide) that I can buy off Ebay include citric acid, oxalic acid, and sulfamic acid. But will these also be effective on copper corrosion, and keep the byproducts in solution?
Additionally, will I need to use any corrosion inhibitors, to prevent the acid for eating away from the raw metal itself? If so, what should I use, and what acids are they compatible with? I'd like to avoid anything that would leave phosphates/silicates/etc coated on the metal.
TL;DR: What (stored-as-solids) acids/liquids can clean corroded copper, that will leave the byproducts in solution? Do I need to use any corrosion inhibitors?
Note: I do not have access to chemical suppliers, so only things commonly available on Ebay and the like please. Additionally, I do not have fume hood, so no toxic fumes too.


texts:
Can any other wavelength of electromagnetic radiation be used?
Why can't gamma radiation be used?


texts:
What kind of a bond is the Hydrogen bond? Is it electrostatic forces of attraction or more like a partial coordinate bond?
What pair of atoms would provide us the strongest Hydrogen bond? If we consider electrostatic forces then HF and HF should be strongest. But how about HF and NH2?


texts: Find the molar percentage of a metal ion from the magnetic susceptibility of a contaminated sample

texts:
I'm trying to find the molar percentage of a $\ce{Cu(II)}$ acetate sample from the magnetic susceptibility of a contaminated sample of mononuclear $\ce{Cu(II)}$ & $\ce{Cu(II)}$ acetate.
The question gives the magnetic susceptibility of the contaminated sample as $867.2 \times 10^{-6}$. I calculated the magnetic susceptibility of the $\ce{Cu(II)}$ acetate to be $865 \times 10^{-6}$.
I have no idea how to go from this to calculate the molar percentage of the $\ce{Cu(II)}$ acetate sample. We're given the temperature of $\pu{250 K}$ and the Boltzmann constant $(k = \pu{0.6950 cm-1 K-1})$.
Please could someone point me in the right direction? I've been going in circles for hours.


texts: Which one, Mulliken charge distribution and NBO, is more reliable?

texts:
Sometimes the Mulliken and NBO turn out to be so different that I can't decide which one I can trust. I've heard that Mulliken is inaccurate, but is NBO always accurate?
And should I use Gaussian or other software to calculate charge distribution? Are there methods more accurate than Mulliken or NBO?

And charge distribution doesn't represent charge density, right?


texts: How Would A Vast Mixture (Like an Ocean) of Ammonia-Water Behave in Terms of Evaporation and Freezing?

texts:
First, I'll go ahead and say I'm not very versed in chemistry. My question comes from my interest in planetary-sciences, specifically the speculation that there are likely exoplanets and moons with surface oceans of water-ammonia. However I can't find much hard info on how a vast body (i.e. ocean) of water-ammonia would behave differently than just water.

In short my question is how might a water-ammonia ocean differ from a "pure" water ocean in terms of:

Ice(s) formation
Evaporation
Changes in water/ammonia ratio based on the above two factors (ice formation and evaporation).

This seems largely like a chemistry question to me. If I'm wrong please let me know which Stack Exchange you think I should post in. :)

Parameters:

5% - 40% ammonia.
Temperature range: -80C to 15C
Atmospheric Pressure: 0.5 bar to 30 bar.

More Info:

I've heard that the freezing and boiling points of the mixed liquid would exist on some continuum between the freezing and boiling points of its constituent liquids (ammonia and water), varying depending on the exact mix ratio and of course pressure. Is that correct?

What I'd like to most wrap my head around is whether the water-ammonia mix would behave as a single uniform liquid, freezing and evaporating at a rate determined by the average of the mix's freezing/boiling point, or whether the ammonia molecules would start to evaporate before the water molecules, and the water molecules start to form ice before the ammonia molecules.

If the later behavior is correct I could imagine an ocean of water-ammonia varying substantially in its water/ammonia ratio from pole to equator thanks to the greater heat near the equator and the ammonia molecules evaporating.

Thanks!


texts: Which is better: iodine number or bromine number?

texts:
The degree of unsaturation of fats can be determined with the help of two type of scale namely iodine number and bromine number.

Generally, iodine number is more preferred over bromine number (Is this statement true? Is it because the Wikipedia article of iodine number is more elaborated than that of bromine number?)

Iodine number is typically found out by using iodine monochloride, $\ce{ICl}$ where the iodine atom gets bonded with the carbon atom having double bond. The more iodine  used up to break the $\ce{C=C}$ bonds,  higher is the iodine number.

$$\ce{-CH=CH - + ICl -> -(I)CH-(Cl)CH - }$$

But in the 4th paragraph of the 1st page of this link, it is written that:

  Iodination
  is an endothermic process, resulting in vicinal diiodides that tend
  to revert to alkenes. Consequently, the most common applications of
  alkene halogenation are chlorination and bromination.

So, in this context, bromination is better and thus bromine number is better than iodine number. The statement contradicts the previous statement i.e. using iodide number.

H.P.Kaufmann method of finding iodine number uses bromine. Is this a better method than using $\ce{ICl}$ considering the disadvantage of iodination?


texts: Odd/Even swap rule for chiral compounds in stereochemistry

texts:
I had this question asked in my exam, where I was supposed to find if this pair is a diastereomer:

Now, I have learnt this rule where: Making odd number of swaps in a molecule means they both are enantiomers, and making even number of swaps means they are identical.
So according to this rule, I made even no. of swaps in the molecule to the right, which means it is identical to the inital molecule that was on the right. Now this newly formed molecule superimposes the molecule to the left perfectly. Hence, in my opinion the two molecules in the picture above should be identical. But the answer given in my answer key is that they are diastereomers, and not identical.
Is there any flaw in my justification?


texts: Do we consider the dissociation of water when dealing with ion concentrations of a solution?

texts:
One mole of hydrated copper(II) sulfate, $\ce{CuSO4 . 5 H2O},$ is dissolved in water. How many moles of ions does the solution contain?
1) 1
2) 2
3) 6
4) 7

The correct answer is 2. Specifically, I'm confused about why the $\ce{OH-}$ and $\ce{H+}$ ions aren't considered.


texts: Why these chemical reactions do not occur?

texts:
I have this list of reactions which don't occur:
$$\ce{MgCl2(aq)} + \ce{K2SO4(aq)}$$
$$\ce{Fe(NO3)2(aq)} + \ce{SnCl4(aq)}$$
$$\ce{Cu(NO3)2(aq)} + \ce{FeBr3(aq)}$$
$$\ce{KCl(aq)} + \ce{CuSO4(aq)}$$

I would like to know why and how can I recognise when a reaction occurs or it does not.

My thought: I think the products are salts, which they remain dissolved in water. In this case reactions would not happen because we are considering an aqueous solution. Am I right?


texts: Is it possible to synthesise ethers from carboxylic acids?

texts:
Is it possible to synthesise ethers from carboxylic acids, and if so, how? By ether I mean an ether in general ($\ce{R-O-R'}$), not just specific examples.

I theorised one could perform Fischer esterification, $\ce{ROH +R'COOH -> RCOOR'}$, and then perform Wolff-Kishner reduction on the carbonyl group. The problem with this theory is that it assumes that the single-bonded oxygen between the $\ce{R}$ and $\ce{R'}$ doesn't influence the reduction process.


texts: Similarities and Differences between Resonance and MCSCF treatments

texts:
Recently, there has been a question by Voldemort concerning different resonance structures of $\ce{NCO-}$, requesting an explanation why one resonance structure would be more preferred than another.
There has been a little discussion on that between ron and Martin - マーチン that took my interest:

ron: "[...] structure #1 ($\ce{N#C-O-}$) is more stable (preferred) than structure #2 ($\ce{^{-}N=C=O}$)."
Martin - マーチン: When talking about resonance structures, I think stable is the wrong word. I agree with your analysis in terms of contribution. Therefore #1 should have the highest contribution of all.

Now while I agree with ron that structure #1 is the most preferred resonance structure (referring to electronegativities), I regret with him concerning his attitude towards the "stability" as Martin does.
But I mainly do this, because I used NBO6 with the Natural Resonance Theory (NRT) keyword on the Natural Bond Orbitals (NBO) produced of an MP2/6-311+G(2d) optimized wavefunction to find the contributions of all relevant resonance structures - $66~\%~(\ce{N#C-O-})$, $30~\%~(\ce{^{-}N=C=O})$ and $3~\%~(\ce{^{2-}N-C#O+})$ - and not because I have a superior understanding on all underlying theories.
For me, the resonance stuff lookes a lot like MCSCF treatment of some VB wavefunction, which means that the complete molecule is described best from it's contributing resonance structures.
Now on a more complete comparison, what are the main similarities and differences between both theories and as they don't exist but are rather part of an explanation, can resonance structures indeed be described as "stable"?


texts: Calculating distance between adjacent planes (hkl) in a simple cubic crystal

texts:
My textbook says the following in a section on Miller indices:

Adjacent planes $(hkl)$ in a simple cubic crystal are spaced a distance $d_{hkl}$ from each other, with $d_{hkl}$ given by:
$$d_{hkl} = \frac{a}{\sqrt{h^2 + k^2 + l^2}} \tag{2.12}$$
where $a$ is the lattice constant. Equation $2.12$ provides the magnitude of $d_{hkl}$ and follows from simple analytical geometry. To generalize this expression, notice that for a plane $(hkl)$ with $hx + ky + lz = a$, the distance from any point $(x_1, y_1, z_1)$ to this plane is:
$$d_{hkl} = \left| \frac{hx_1 + ky_1 + lz_1 - a}{(h^2 + k^2 + l^2)^{1/2}} \right| \tag{2.13}$$
Hence when that point is at origin $(0, 0, 0)$, we find Equation $2.12$ back.
Example 2.1: With $a = \pu{5 Å}$, we find $d = a = \pu{5 Å}$ for $(100)$ planes and $d = \frac{a}{\sqrt{2}} = \pu{3.535 Å}$ for $(110)$ planes.

I'm confused as to how the author calculated sample 2.1. For instance, if we take $a = \pu{5 Å}$ for $(100)$ planes, then we get
$$d_{hkl} = \left| \frac{x_1 - \pu{5 Å}}{(1 )^{1/2}} \right| = \left| x_1 - \pu{5 Å} \right|$$
So how did the author get $d = a = \pu{5 Å}$?
I would greatly appreciate it if people could please take the time to clarify this.


texts: Does Le Chatelier's principle apply to the gas inside an air mattress?

texts:
While sleeping on an air mattress yesterday a thought occurred to me. I had to re-inflate the air mattress since it was getting rather low and after it had a good stiffness to it, I went to sleep. The next morning I noticed that a lot of the pressure that I put into the air mattress had left and I remembered Le Chatelier's principle which says that gases in a closed system will convert to the least number of molecules possible if the pressure is increased.

So this is my thought:

Breathing into the air mattress had added moles of gas to a closed system (the air mattress).
Lying on the air mattress increased the pressure of the system.
Given Le Chatelier's Principle, the gases should have transitioned to the lowest number of moles to relieve the pressure introduced on the system.

The thing I'm not sure about is if there are any equilibrium reactions for the gases in our atmosphere that will actually do this. Considering the makeup of our atmosphere, does Le Chatelier's Principle apply to the air inside an air mattress?


texts: How to determine an unknown gas in a tube with a massless piston at equilibrium conditions?

texts:
There is a massless piston that can move freely in a horizontal tube that is closed at both ends. To the left, there is a sample of helium gas at $300~\mathrm{K}$ and $4~\mathrm{atm}$. To the right, there is a sample of an unknown gas $\ce{X}$ at $500~\mathrm{K}$ and $2~\mathrm{atm}$. At equilibrium, the piston is located at 1/9 the length of the entire piston from the right side. The molecules of $\ce{X}$ are homonuclear. What is most likely the identity of $\ce{X}$?

(From Chemistry Olympiad)

I'm confused by the equilibrium part. I tried $PV = n\mathcal{R}T$ to find the ratio of moles. But without molar mass, how do you solve for it? How would you solve it?


texts:
A trivial research in atoms and their basic theories led me to this term: "isotones"
Nuclides sharing the same number of neutrons but different atomic numbers.
A simple request or shall I say, quest:
please indicate me to any feasible similarities existing between isotones and please, DO NOT use jargon.


texts: More than one way of balancing a chemical equation

texts:
My textbook had this question on balancing chemical reactions

  Ozone reacts with nitric oxide to give nitrogen dioxide and oxygen gas

Here's how I balanced it: $$\ce{O3 + NO -> NO2 + O2}$$

However I realised that the equation is also balanced if I write it as: $$\ce{2O3 + 4NO -> 4NO2 + O2}$$

and when it is written as: $$\ce{3O3 + NO -> NO2 + 4O2}$$

This seems wrong as I am sure that there cannot be more than one way of balancing a reaction but I do not have a satisfactory explanation. What is going wrong here?


texts: What is the hybridisation of carbon in transition state in SN2 mechanism?

texts: Normally, a carbon atom is $\ce{sp^3}$ hybridized, whereas in a transition state five bonds are present, then what's the hybridisation of carbon?


texts:
I came across this question:

  Which is the most stable resonating structure of p-nitrosobenzene
  among the following?

I have been taught about the priorities for resonance structure stability as follows:

  Complete octet $\rightarrow$ more stable
  Uncharged $\rightarrow$ more stable
  Lower formal charge $\rightarrow$ more stable
  Less separation between opposite charges $\rightarrow$ more stable
  Negative charge near more electronegative atoms and positive charge near less electronegative atoms $\rightarrow$ more stable

So according to the above rules, (b) and (c) are the among the most stable. Bu then applying rule #4 above, (b) should be more stable, because here each positive charge is in vicinity of negative charge.

However the answer given is (c). Why is this?


texts:
This the structure of Dolomite.

Can someone explain this structure to me?( like what are the blue, yellow etc atoms are? why are they arranged this way?)

Any help would be appreciated.


texts: How can I find pKa from a titration curve?

texts: I am fully aware that the pKa is the pH at half the equivalence point, but are there some programs or methods I could use to accurately estimate the pKa without manually drawing lines on the graph?


texts: How does the inductive effect, explain the reactivity of tertiary alcohols with halogen acids?

texts:
The reactions of primary and secondary alcohols with halogen acids ($\ce{HX}$, where $\ce{X}$=halogen) require the presence of a catalyst, $\ce{ZnCl_2}$. With tertiary alcohols, the reaction is conducted by simply shaking with concentrated $\ce{HCl}$ at room temperature. Which mean that, tertiary alcohols are more reactive than primary and secondary alcohols. The reason is said to be, due to the inductive effect.

I don't know how the inductive effect would explain that, tertiary alcohol is more reactive than primary and secondary.


texts: Why shouldn't lithium batteries be discharged below 50%?

texts:
I know both from online websites and from experience that discharging a li-ion battery below 50% greatly decreases its life and capacity.

But why is it so?


texts: Will there be change in electronegativity difference in C-O and C=O?

texts:
Is there any change in EN difference in C-O and C=O. If yes, why?
Does EN difference change if its bond is changed to single, double, or triple?


texts: Consider a concentrated dye solution, say 10µM of Rhodamine 6G in water, which is rapidly diluted down to 10nM in an open container. I'm trying to estimate the (presumably minute) temperature change, assuming both solutions (dye and water) are initially at the same room temperature. I believe dilution increases entropy ever so slightly, but I'm struggling to turn this statement into a quantitative temperature change. Specifically, how do I calculate the change in entropy? Once I know this, the change in temperature should be straight-forward.


texts: Given the volumes: determine the pH and the final temperature of a mixture knowing only the initial pH and the temperature of the un-mixed components

texts:
I have a pretty basic question but the last time I took Chemistry was in 2007.  I am studying the Navy's Nuclear study guide for their interviews and one of the question I am faced with is below.

Determine the final pH and temperature when the following two solutions are mixed together in a $\pu{3L}$ container.
Sol A: $\pu{2L}$, pH = 3, and $\pu{80 ^\circ F}$
Sol B: $\pu{1L}$, pH = 5, and $\pu{40 ^\circ F}$

Would this be as simple as $(2/3) \cdot 3 + (1/3)\cdot5$ for the pH and $(2/3)\cdot80 + (1/3)\cdot40$ for the temperature?


texts: Solubility curve for sodium tetraborate in water

texts:
What is the solubility curve for sodium tetraborate decahydrate ($\ce{Na2[B4O5(OH)4]·8H2O}$), otherwise known as borax, in water ($\ce{H2O}$)?

Additionally, what is the solubility of the aforementioned substance, borax, at $\ce{100°C}$?


texts: How to choose alcohol solvent for organic extraction?

texts:
Assuming I have an organic substance that is known to be "soluble in alcohol" (e.g. capsaicin) I want to extract, which alcohol should/can I use? I know that both ethanol and methanol are commonly used, but what about:

isopropanol
glycerol
n-Butanol
1,4-Butanediol
tert-Butyl alcohol
1-Pentanol
tert-Amyl alcohol

In general, which alcohols are suitable/unsuitable for organic compound extraction (e.g. which should be the best solvent in terms of amount of solute dissolved in given volume of solvent), and why? Is there any a priori way to determine e.g. if isopropanol extraction will be OK for a given "soluble in alcohol" organic substance?

Note: I am aware of this discussion, but it doesn't cover the specific nature of alcohol extraction.


texts: Maximum Local Value for the Electron Density

texts:
So the electron density is the function $\rho(\vec x)$ that associates a value of electrons per cubic angstrom, to each point $\vec x$ in the 3D space.
This information tells us how likely it is to find electrons at specific regions of space within a system. Integrating $\rho$ over a particular volume $\mathcal{V}$ gives us the number of electrons likely to be found, at any given moment, inside $\mathcal{V}$, denoted $n[\mathcal{V}]$.
$$
\tag{2}
\label{eq:rho-integrate-volume}
n[\mathcal{V}] = \int_\mathcal{V} \rho(\vec x) \mathrm{d}\vec x
$$
Integrate over the whole space $\Omega$ where the system is and you get $N$, the total number of electrons in the system.
$$
\tag{3}
\label{eq:rho-integrate-omega}
N = n[\Omega] = \int_\Omega \rho(\vec x) \mathrm{d}\vec x
$$
Electrons repel one another and are attracted to the atomic nuclei. I believe that particularly high values of $n[\mathcal V]$ are unlikely because as you pack more and more electrons in the same region, their repulsion would start to overpower their attraction to the nuclei, meaning the electron density would likely spread out more.
So my question is Is there a maximum value for $n[\mathcal{V}]$ above which the mutual repulsion of electrons would mean the density was unreal?
I understand that such a value would vary depending on promixity to the atomic nuclei (which would shield electrons from their own mutual interactions) and the size of the integrated volume $\mathcal{V}$. What I mean is if there is a known relationship between these factors that would give us the maximum amount of electrons allowed inside a particular region of space.


texts: How can you use ICE tables to solve multiple coupled equilibria?

texts:
If I have a problem involving multiple coupled equilibrium reactions, such as

  Calcium fluoride, $\ce{CaF2}$, has a molar solubility of $\pu{2.1e−4 mol L−1}$ at pH = 7.00. By what factor does its molar solubility increase in a solution with pH = 3.00? The p$K_{\mathrm{a}}$ of $\ce{HF}$ is 3.17.

The relevant reactions are:

$$\ce{CaF2(s) <=> Ca^2+(aq) + 2 F-(aq)}$$ and
$$\ce{HF(aq) <=> H+(aq) + F-(aq)}$$

They are coupled because fluoride occurs in both of them.

Is there a way to use ICE tables to organize the information (stoichiometry, initial concentrations, mass balance) as a way to solve the problem?

For example, I could try to set up one ICE table for each reaction (the column for $\ce{H+}$ is strange because in the problem, the pH is set to a value through an unspecified mechanism):

$$
\begin{array}{|c|c|c|}
\hline
 &[\ce{Ca^2+}]  & [\ce{F-}]  \\
\hline
I &  \pu{2.1e−4} & \pu{4.2e−4} \\
\hline
C &  +x  & +2x  \\
\hline
E &  \pu{2.1e−4}+x & \pu{4.2e−4}+2x \\
\hline
\end{array}
$$

and

$$
\begin{array}{|c|c|c|}
\hline
 &[\ce{HF}]  & [\ce{H+}]  & [\ce{F-}]  \\
\hline
I &  0 &  \text{N/A} & \pu{4.2e−4} \\
\hline
C &  +x &\text{N/A} & -x \\
\hline
E &  +x & 10^{-3.00} &  \pu{4.2e−4} - x\\
\hline
\end{array}
$$

However, how do the fluoride concentrations "talk to each other" in the two tables? Is the $x$ in one table the same as the $x$ in the other table?


texts: Cyclohexane derivative formation of carambolaflavone using a Lewis acid catalyst

texts:
The scheme below summarizes the results from a study into the optimum conditions needed for a key step in the synthesis of the proposed structure of carambolaflavone, a natural product that has antidiabetic properties. Note that $\ce{Sc^3+}$ acts as a Lewis acid in these reactions.

I'm very confused about how the acid is coordinating to the Benzene derivative here?


texts: Basic behavior of ammonia in aqueous medium

texts:
Thanks to the reversible reaction
$$\ce{NH3 + H2O <=> NH4+ + OH-},\tag{R1}$$
we know that ammonia acts as a weak base. However, I was wondering why it ends up forming ammonium $\ce{NH4+}$ and not azanide $\ce{NH2-}$ according to
$$\ce{NH3 + H2O <=> NH2- + H3O+}.\tag{R2}$$


texts: Which are more reactive lanthanides or aluminium?

texts: I am not sure whether to consider the standard reduction potential or ionisation enthalpy.Which would be more reactive out of the lanthanides and aluminium


texts: Gaussian scan function help for constructing input file

texts:
I have the cartesian coordinates for two molecules that are in a stacked position and I want to be able to calculate the potential energy at 0.2 angstrom steps from when the top molecule is 3.0 angstroms to 7.0 angstroms away in the z direction. My professor told me gaussian has a scan function to do this but I'm having trouble figuring some things out. I have the basis set/ correlation methods I need to use and the cartesian coordinates for all the atoms when they are arranged 3.0 angstroms apart. I tried following this site's advice;

 but I'm not sure I constructed the input file correctly. Here is what I have

.

From my understanding, this should just move up all of the atoms of the top molecule by 0.2 angstroms in the Z direction.

Questions:

Do I just throw this stuff anywhere into the input file? What about the original cartesian coordinate array? Surely it has to stay since the "step" array calls back to atoms 101-112. Do I have to change any other commands? The only parameters set are the resource limits and "#P BP86/6-311++G**"

Update:

I think I may have been unclear. I have already optimized my two molecules. One is a nanotube and the other is an arene and my task was to basically generate this plot. I'm trying to find the distance apart where the two molecules are stabilized. Before, I just ran the "#P BP86/6-311++G**"" with my arene @ 3.0 angstrom apart and made new input files changing the arene z coordinates in 0.5 angstrom increments but I can't capture that potential energy well. I decided to try smaller increments to increase the resolution but I have quite a few more situations to test so I wanted to just have Gaussian change the increments and recalculate the potential energy.

  Thankfully a full relaxed scan is not necessary in most cases. Oftentimes a nice little rigid scan will give you a decent result. Have a look at the scan keyword. The only downside to this approach is, that you need a z-matrix to make it work. And putting your brain to that task is also a bit tedious.

That's what I initially came across but with ~100 atoms, I just let Chemcraft generate the z matrix from my cartesian coordinates. The thing is, I'm not sure quite how to edit the z-matrix (relevant part below) with the scan commands.

Specifically I want to keep all bond angles the same but move atoms 101-112 in 0.2 A steps in the z direction, and calculate the potential energy.

I guess my question is now if this is a plausible approach. I'll try to look up how to construct the proper z-matrix if that is indeed the best way to do things.

Thanks @Martin


texts:
I was trying to make a $2\text{M}$ solution at $\text{pH}\, 7.5$ of Betaine $\ce {HCl}$.
I started by weighing out the appropriate amount of Betaine $\ce {HCl}$, added some water and started stirring. At this point, the $\text{pH}$ of the solution was $\sim1-2$.
I went on to titrate the solution with $\ce {NaOH}$.
At about $\text{pH}$ $3-4$ the betaine $\ce {HCl}$ was completely dissolved.
as I added more base, I noticed that the solution began to warm up and give off a some sort of a "plasticy" smell and foamed a little bit. This began to happen at around $\text{pH}$ $5.5-5.7$.
It seems to me that the Betaine $\ce {HCl}$ is somehow reacting at high $\text{pH}$.
I was wondering if someone can explain what may be happening to the Betaine $\ce {HCl}$.


texts: Hybridization of nitrogen in trisilylamine, (SiH3)3N?

texts:
I want to know the hybridization of the central atom in $\ce{(SiH3)3N}$.

I think it should be $\mathrm{sp^3}$, because $\ce{N}$ is attached to three silicon atoms and one lone pair. But actually it is supposedly $\mathrm{sp^2}$.

How is this so?


texts: Does nitric acid release hydrogen only when reacting with Mg and Mn?

texts: $\ce{HNO3}$ always reduces its anion to give nitrogen containing compounds ( $\ce{NO2}$, $\ce{NO}$, and even $\ce{N2O}$) when reacting with metals, but with $\ce{Mg}$ and $\ce{Mn}$ it releases $\ce{H2}$. Is there a specific reason for this variation?


texts:
I know that there is 2:6400 deuterium and hydrogen molecules respectively in water.

When electrolysis is done, hydrogen and oxygen will be obtained. The hydrogen obtained should contain small amounts of d2 and t2.

Is there a way to separate it by diffusion or effusion (or any other way)?


texts: If fluorine and cerium ion have more oxidising power than KMnO4, why is KMnO4 more popularly used as an oxidising agent?

texts: It is quite clear from the electrode potential values that $\ce{F2}$ and $\ce{Ce^{4+}}$ are better oxidizing agents that $\ce{KMnO4}$.


texts: What is buffer capacity and how can a buffer "run out"?

texts:
I'm a little confused on something:
A buffer has a certain capacity and then runs out.
But, if the buffer is given by: $$\ce{A- + H2O <=> HA + OH-},$$ when the $\ce{A-}$ reacts with the water, the reaction shifts to the left. So how can it "run out"? If $Q$ just keeps becoming $0$, shouldn't the reaction keep shifting to maintain $K$? Does the right side, perhaps, approach $0$ as it keeps decreasing in concentration to maintain $K$, but it can never become $0$ molar, because that wouldn't maintain $K$?
I guess if $\ce{H2O}$ was "aqueous"/had a concentration and was therefore used in the $K$ expression, this the $K$ would always be maintained.
But how does the buffer "run out" of $\ce{A-}$ to react when $\ce{H2O}$ is liquid (not aqueous)? It doesn't make sense as wouldn't the reaction always adjust to make more $\ce{A-}$ to maintain $K$?


texts: What is the basis for naming the p-orbitals with reference to the Cartesian coordinate system as x, y, and z?

texts:
There are 3 p-orbitals per subshell, which are $p_x$, $p_y$ and $p_z$. As well as there are 5 d-orbitals, which are $d_{xy}$, $d_{yz}$, $d_{zx}$, $d_{x^2-y^2}$, and $d_{z^2}$.

My Question: What is the basis for choosing the axes as $x$, $y$, and $z$? Can we rearrange the axes, suppose lets replace $x$ with $y$, $y$ with $z$, and $z$ with $x$. Then we will have the d-orbitals to be $d_{yz}$, $d_{zx}$, $d_{xy}$, also you would get $d_{y^2-z^2}$, and $d_{x^2}$, orbitals. Why do we choose that particularly?


texts: How to prove that the orientation of the atomic orbitals in the superposition $\psi= a\psi_{1} + b\psi_{2}$depends on the coefficients $a$ & $b$?

texts:
Hybridisation is a quantum superposition of orthogonal atomic orbitals; for instance
$$\newcommand{\k}[2]{\langle #1 \lvert #2 \rangle}
\psi_{sp^3}= c_1\psi_{2s}+ c_2\psi_{2p_{x}} + c_3\psi_{2p_y} + c_4\psi_{2p_{z}}.$$

It is a quantum superposition which implies the coefficients $c$ to be the probability amplitudes for finding the electron in respective atomic orbital provided that it is prepared in $\lvert\psi_{sp^3}\rangle$(provided $\sum_{i=1}^4 c_1^2 =1$) that is, $$c_1= \k{\psi_{2s}}{\psi_{sp^3}}, \\ c_2= \k{\psi_{2p_x}}{\psi_{sp^3}},\\ c_3= \k{\psi_{2p_y}}{\psi_{sp^3}},\\ c_4= \k{\psi_{2p_z}}{\psi_{sp^3}}.$$

Up to this, I could easily understand this as it was just like some other superposed state often encountered in QM like $\lvert\phi\rangle = \lvert i\rangle c_i + \lvert j\rangle c_j + \lvert k\rangle c_k$ where $c_i = \k{i}{\phi}.$

But, here in the case of hybridisation, they are much more than mere comples numbers that are the amplitudes of the electron to find it in one of the base states that is the associated atomic orbitals when being prepared at the hybridised state. It is evident from Peter Atkins' words:

  The coefficients in the hybrid have been chosen to give the correct directional properties of the hybrid. The squares of the coefficients give the proportion of each atomic orbital in the hybrid.

Also, the snapshot$^1$ below shows how for different values of coefficients, the spatial orientation is changed.

That means the coefficients  direct the spatial orientation of the atomic orbitals that are the base states for the superposition or hybridisation.

Is there any mathematical deduction that shows the orientation of the atomic orbitals in the superposition depends on the coefficients $c_i$?

I'm basically not understanding how these coefficients, which are rather probability amplitudes, would involve in determining the spatial orientations of the atomic orbitals. Can anyone explain me why these probability amplitudes influence the orientation of the atomic orbitals? Also, what is the mathematical proof of this?

$^1$The snapshot, above, is taken from Principles of Physical Chemistry
 By Hans Kuhn, Horst-Dieter Försterling, David H. Waldeck.


texts: Is this a possible explanation as to why sigma bonds are stronger than pi bonds?

texts:
Sigma bonds form due to the axial overlap of two orbitals whereas pi bonds form due to their lateral overlapping. Since the former is more effective, we can say that sigma is stronger than pi. We mean that the orbitals overlap to a further extent in sigma bonds and not as much in pi bonds(...or at least that is what I infer). To me this sounds like a circular proof/explanation, so I thought up another way to understand it.

In a sigma bond, the electron cloud of one atom is attracted to the nucleus of the other atom's nucleus.This happens because of the electrostatic forces of attraction between the positively charged protons in the nucleus of one atom and the negatively charged electron cloud of the other atom. The attractive force causes the electron clouds to the atoms to overlap, despite the fact that the electron clouds should repel each other.  However, the electrons start to repel each other after a certain extent of overlapping has occurred. (Because the repulsive forces between the two nuclei and the electron clouds negate the attractive forces)

In a pi bond, there is no positively charged nucleus that would attract the electrons, so there must be another factor favoring the bond formation.
Since I haven't studied the quantum mechanics of bonding yet, my best guess is that the pi bond (or lateral overlapping) occurs because of the pairing of electrons.
So this means that sigma bonds are stronger because of electrostatic forces, which consequently causes more effective overlapping than pi bonds.

Is my reasoning correct to some (if any) extent?


texts: Fischer Esterification of the Unsaturated 3-Butenoic Acid with Methyl Alcohol

texts: I am attempting to perform a Fisher esterification of 3-butenoic acid (vinyl acetic acid). I believe that this should theoretically work and not disturb the unsaturated region of the molecule, but I'm not certain. Has anyone had any practical experience with this in the lab or seen any literature referencing a Fischer esterification being performed on an unsaturated acid? Theoretically, since the esterification is being performed with anhydrous methanol with a sulfuric acid catalyst the acid-catalyzed hydration should not be possible; however, as the reaction progresses, water present in the reaction mixture may hydrate the alkene. Will this not be an issue since there will still be a large excess of methanol or will I need to find a physical method to remove the water from the reaction as it forms? Given, a Dean-Stark apparatus cannot be used. I'm thinking about using molecular sieves to remove any trace of water as it forms in situ but I don't know if this would work? Has anyone ever attempted this or something similar?


texts: Can color-changing leuco dyes be used to indicate when a certain molecule binds to another in a textile fabric?

texts:
Thermochromic leuco dyes change color when the temperature changes. I want to use leuco dyes to make a color-changing fabric. However, instead of using temperature to induce color changes, I want the color to change when a molecule woven into the fabric binds to another molecule, sort of like a lateral flow/pregnancy test.
Can leuco dyes be used to signal when a molecule binds to another and cause a color change in textiles/fabric?


texts: How does increase in volume change the speed of reaction in production of NO2?

texts:
$$\ce{2 NO + O2 <=> 2 NO2}$$

I understand that increasing the volume $×2$ means lower pressure so production of $\ce{NO2}$ is slowed down, but when asked how to express this mathematicaly I can't get to the correct value, which is either $4$ or $8.$ I don't see how inserting $1/2$ in $v = Δc/(2×Δt)$ can give anything close to the offered solutions.


texts:
I wanted to ask a question about acid catalysed hydrolysis.

I learnt in an introductory course to Physical Organic Chemistry that there are different ways that an ester can be hydrolysed acidically:

  $\ce{A_{AC}1}$
  $\ce{A_{AC}2}$
  $\ce{A_{AL}1}$
  $\ce{A_{AL}2}$

There are different ways that esters can be hydrolysed:
– catalysis by acids (A) or bases (B)
– cleavage of acyl-oxy (AC) or alkyl-oxy (AL) bonds
– the molecularity of the key step (1 or 2).

Using Acids (A) there are 4 different ways to hydrolyse an ester using acid catalysis:

  $\ce{A_{AC}1}$ Cleavage of Acyl-Oxy Bond Unimolecular
  $\ce{A_{AC}2}$ Cleavage of Acyl-Oxy Bond Dimolecular
  $\ce{A_{AL}1}$ Cleavage of Alkyl-Oxy Bond Unimolecular
  $\ce{A_{AL}2}$ Cleavage of Alkyl-Oxy Bond Dimolecular

An explanation can be found here.

But consider this question, with the marking scheme given below:

Our professor did not mention anything regarding how to choose which type of hydrolysis takes place. From this question, he states and goes further onto mention that either $\ce{A_{AC}1}$ or $\ce{A_{AC}2}$ can take place, but no other.

I'm looking at these structures and thinking

Why can't $\ce{A_{AL}1}$ or $\ce{A_{AL}2}$ take place for these two? Why must it be the two given in them marking scheme?


texts: Why perborate is greener bleaching agent?

texts: All I know is, perborate degrades into supposedly less harmful compounds.  But what exactly happens that it is considered greener? Consider say perborate vs. hypochlorite.  Why perborate is "greener"?


texts: Should the measurement uncertainty be included in the random uncertainty?

texts: So, the other day I was carrying out a titration and got the titres $33.4cm^3$ and $33.3cm^3$. I calculated the random uncertainty to be $0.05cm^3$. Now, the burette itself had an uncertainty of and I'm wondering whether I should add these two uncertainties together to find the uncertainty for the titres. Also, if I have to use the average of the titres to calculate the percentage uncertainty or whether I need to calculate the percentage uncertainty individually for the titres.


texts: Is there a reliable way to determine if a chemical system is more suited to be calculated using a multireference method instead of DFT?

texts:
Some time ago I recall hearing a professor say that looking at a DFT result (I don't remember exactly what, a TD-DFT, spin contamination etc...), he could tell that the system was multireferenced.

My question is: do we have anything in a DFT calculation that is indicative of a multireference system?


texts: Easy to perform enantioselective derivatization of cyclohexenone-like structures

texts:
I'm looking for easy-to-use derivatizations of cyclohexenone-like structures. In fact, I'm working with 3-ketosteroids having the same double bond in the A ring as cyclohex‐2‐en‐1‐one has. The only widely used derivatizations produce two enantiomers; this is not optimal for my application.
I know that there are some Michael additions that are relatively enantioselective with reported enantiomeric ratios of 99:1. Unfortunately, according to this manuscript by Muniappan Thirumalaikumar, these Michael additions require sophisticated catalysts that first have to be synthesized. As we are an analytics lab and not an organic synthesis lab and the derivatization should be applied in routine lab experiments, I'm looking for easy and relatively fast reactions producing considerable enantiomeric excesses.
Feel free to provide any idea, even if you're not sure.
Reaction requirements:

relatively fast (up to 24 h)
"normal" chemicals that can be purchased as is
the derivatizing agent should carry an amino moiety or, alternatively, a permanent positive charge


texts: Acidity order of acetone, methyl acetate and N,N-dimethylacetamide

texts:
Why is the acidity order true?
  $$\ce{CH3COCH3} > \ce{CH3CO2CH3} > \ce{CH3CON(CH3)2}$$

I deduced that in methyl acetate and N,N-dimethylacetamide there is a −I effect of the methoxy group, $\ce{N(CH3)2}$  and a +R effect, too so the attached keto-carbon develops a positive charge and the conjugate base becomes unstable due to the +R effect of methoxy and $\ce{N(CH3)2}$ groups.

Is my logic right?


texts: What are the organic reactions that are taking place in this reaction?

texts: I know that A is the product of a Knoevenagel condensation between the aldehyde and the diethyl malonate, due to the acidic protons of the latter, but I don't know what the reaction between that product and potassium cyanide would be.


texts:
Primary Cells - pH changes during discharge

Alkaline Cell:

Manganese Dioxide Zinc Alkaline Cell

Anode (-)
$\ce {Zn(s) + 2OH^{−}(aq) → ZnO(s) + H2O(l) + 2e^{−}}$

Cathode (+)
$\ce {2MnO2(s) + H2O(l) + 2e^{−} → Mn2O3(s) + 2OH^{−}(aq)}$

Overall
$\ce {Zn(s) + 2MnO2(s) → ZnO(s) + Mn2O3(s)}$

$\ce {OH-}$ ions are consumed at the anode
$\ce {OH-}$ ions are formed at the cathode
$\ce {same[OH^{−}]}$
pH - no change

Is this correct? Do pH changes occur during the discharge process?


texts:
$$\ce{e- + H2O -> [H$\cdot$] + HO-}$$

I was a little confused on the notation of the hydrogen in brackets ([H]) in the product side of the reaction. Why is there a dot next to it and what does it mean? Is it saying Hydrogen gas?

Also, what will be the reduction potential of this reaction?


texts:
In this image, does the arrows indicate correct rate of reactions? The upper arrow is longer and lower is shorter.

According to me Chair is more stable than Twist Boat. Does axial and equatorial arrangement of the two -C(CH3) groups play a role?


texts:
Why is $\ce{Pb^2+}$ present both in Group I and II of the basic radicals?
Is it related to the solubity product of its salts?


texts: How to determine the percentage of iron(II) and iron(III) in a solution?

texts:
Outline a plan of an experiment to determine the percentage of iron
  present as iron(III) in a solution containing $\ce{Fe^3+(aq)}$ and $\ce{Fe^2+(aq)}$
  ions. You are provided with zinc, a standard solution of potassium
  dichromate(VI) and dilute sulfuric acid. How you would use the zinc and how you would calculate the
  final answer.

So I know that the following equations will be involved

$\ce{2Fe^3+ + Zn -> 2Fe^2+ + Zn^2+}$
$\ce{6 Fe^2+ + Cr2O7^2- + 14 H+ → 6 Fe^3+ + 2 Cr^3+ + 7 H2O}$

I am very unsure on the method to use, I know that I can titrate a sample of the solution against $\ce{K2Cr2O7}$ to eliminate $\ce{Fe2+}$ ions, but I am clueless on how to proceed after.


texts: Heating CrCl3(bpy)3 — isomerism and ligand exchange

texts:
$\ce{CrCl3(bpy)3}$ (A) when heated forms (B) which has the formula $\ce{CrCl3(bpy)2}$ and has one free $\ce{Cl-}$ per mole of (B). B can react with ethylene diamine ($\ce{en}$) to form (C) which has the formula $\ce{CrCl3(bpy)2(en)}$.
(B) can also be converted into (D) which also has the formula $\ce{CrCl3(bpy)2}$ but cannot react with $\ce{en}$.
Identify compounds A–D and draw their structures

I know that B is cis-$\ce{[CrCl2(bpy)2]Cl}$
C is $\ce{[Cr(bpy)2(en)]Cl3}$. The $\ce{en\bond{->}metal}$ bonds are where the $\ce{Cl-}$ ions in B are.
D is the trans isomer of B.
What I dont understand is how you're meant to know what A is. I assume it's $\ce{[Cr(bpy)3]Cl3}$ as a later part of the question asks about relative molar conductivity of A and B.
Why would heating that cause a $\ce{bpy}$ to leave the complex and two chlorides to replace it? Or is it $\ce{[CrCl2(bpy)2]Cl(bpy)}$ in which case, why does heating it not form the more stable complex I've stated above?


texts:
I have been wondering on this for quite a while. Consider aliphatic monoaldehydes. If I oxidize them, we get corresponding monocarboxylic acids. We can use certain oxidizing agents to perform the reaction.

For all the possible aliphatic aldehydes, it involves breaking a $\ce{C-H}$, and the formation of the $\ce{C-O}$ and a $\ce{O-H}$. I did calculations and got the enthalpy change for such a process to be $\pu{412kJ/mol}$.

My main motive is to find the electrode potential for the process. Unfortunately, I cannot determine the entropy here, although I don't think the side chain would matter much.

Here's my question. Does the oxidation for all the aliphatic monoaldehydes to carboxylic acids have the same value of electrode potential? In all the cases, it's the same bonds broken and same bonds formed, so I cannot see why the electrode potential should drastically vary for different aldehydes.

My apologies, I was unable to find a $\Delta\text{G}$ value table for such processes.


texts:
I have noticed that liquid $\ce{O2}$ (I clarify it as $\ce{O2}$ because oxygen exists in several other forms which have different colors in the liquid state than $\ce{O2}$) has a light blue color to it.

In the solid state it has a light blue color like it does in the liquid state and then finally a red color if enough pressure is applied. It can also be pink, black, or metallic again depending on the pressure and temperature.

Does it also have a light blue color in the gas phase?


texts: Please explain why dioxygen difluoride is so dangerous

texts:
I just read this article that mentioned that dioxygen difluoride is very dangerous. The terms it uses are "awful", "violently hideous" and "deeply alarming".

But I couldn't get a handle on exactly what it would do that warrants those descriptions.


texts: Is pyrite (FeS₂) an ionic or a covalent compound?

texts:
I have searched all over the web and found a lot of diverse explanations, but none of them are concluding exactly whether $\ce{FeS2}$ (solid - pyrite) is a covalent or an ionic compound.

From electronegativity, it should be covalent as the $\Delta\chi=0.7$ which is less than $1.5$ and thus said to make covalent bonds and therefore be a covalent compound.

From the definition of ionic bonds, which are bonds between a metal and a non-metal element (whereas covalent bonds are bonds between non-metal elements), it should be an ionic compound.

Does someone know which of those is 'true', or better, if there is another, more detailed explanation?


texts: What would be the product (B) in the following sequence of reaction?

texts:
Here is how I approached this:
As we know, alc. KOH results in dehydrohalogenation of the compound which takes place as an anti elimination. And then, we're simply conducting halogenation of the compound which would result in a dibromo substituded product.

Where I'm facing problems is deciding the final orientation of the product. How will we represent the product in the fischer representation as the initial reactant is given in its fischer representation as well.

For reference, here's the product (B) given in my book:


texts: Equilibrium: Effect of change in composition and value of Kp, Kc on changing pressure

texts:
Di-hydrogen gas is obtained from natural gas by partial oxidation with steam as per following endothermic reaction:

  $CH_4{_{(g)}}+H_2O_{(g)} \ce{<=>} CO_{(g)}+3H_2{_{(g)}}$

  How will the values of $K_p$, $K_c$ and composition of equilibrium mixture be affected by increasing the pressure ?

Now,

1) According to this answer $K_c$ only changes on changing temperature i.e. unaffected by pressure.

2) According to Wikipedia the article "Pressure dependence" says, "...However, the composition at equilibrium will depend appreciably on pressure when:

1)the pressure is changed by compression or expansion of the gaseous reacting system, and
2)the reaction results in the change of the number of moles of gas in the system....."

here wiki is using term $K_p$ to denote equilibrium constant. Now the "composition of equilibrium" means $K_p$ and not $Q_p$ because its taking at equilibrium, so the $K_p$ changes with pressure.

3) I have studied that on increasing pressure the reaction shifts the side with less number of sum of  gaseous atoms in the reaction formulae. I know from this question that composition of equilibrium is different from "the side at which the reaction shifts". So it seems my study isn't useful here in deciding the composition of equilibrium

So my question is how will the values of $K_p$, $K_c$ and composition of equilibrium mixture be affected by increasing the pressure ?
Does one change and the other remains unaffected and isn't the composition of equilibrium directly related to $K_p$ and $K_c$

Are dependencies of $K_p$ and $K_c$ different for change in pressure.


texts: How do Shaving Creams, Foams, Soaps ensure cut Hair Fragments that stick & clump between Safety Razor blades are easily washed away?

texts:
This is my first post on Chemistry SE and I figure it's pretty chemical oriented.

On Sustainability SE we were trying to find "organic & natural" alternatives which are okay for lubrication & moisturizing (don't really care about foaming etc), but so far we have one key problem:

Hair fragments clumping and getting stuck in between 3-4 blades of a safety razor and not easily washing out using water, which is not as much an issue with commercial shave products.

Is it some (one or more) active ingredients/chemicals that make it happen or some other chemical phenomenon by which this works?


texts: Separating nickel coin into copper and nickel components

texts:
I'm trying to create a high school level lab in which we separate the metals in an alloy. The objective is to understand and apply standard reduction potentials, and also to do some extra redox reactions to reclaim solid metals. Plus I think it might be fun!

My plan was to simply submerge nickels in an acidic solution. Theoretically, as long as I don't use nitric acid, the nickel will dissolve and leave the solid copper. I tried it out in the fume hood (1 nickel, 100mL 5M HCl solution), but didn't see the telltale blue/green of nickel ions. I tried sanding the nickel, in case there was an inert oxide layer. For a few minutes, I saw a tiny bit of hydrogen evolution, then the sanded surface turned black.

I read that magnesium is sometimes added to coins for corrosion resistance, which is probably why I'm having problems. Does anyone have suggestions to make this lab possible? Maybe some electrochemistry?


texts: Is levomenthol superior to Menthol as a pain killer in humans and what are the ways to determine this?

texts:
I desire to learn whether levomenthol is superior to Menthol as a pain killer in humans.

I didn't find a wiki article about levomenthol and the article Menthol doesn't mention this molecule.

The chemical formulas are the same but I understand that the only difference is the spatial position of chemical bonds between the atoms, as can be learnt in pubchem:

https://pubchem.ncbi.nlm.nih.gov/compound/Menthol
https://pubchem.ncbi.nlm.nih.gov/compound/l-Menthol

My problem

I don't know what are the main ways for chemists to decide which one should work better in humans but hope for a simple explanation for non chemists.

I thought about this after reading that Strepsils, the famous British sore throat lozenges, contain levomenthol.

I think about this because I know some other medicines are "levo" versions of others (for example, cetrizine and levocetrizine).

My question

Is levomenthol superior to Menthol as pain killer in humans and what are the ways to determine this?


texts: Oxidative cleavage of 2-methylcyclohexa-1,3-diene

texts:
What are the products of oxidation of 2-methylcyclohexa-1,3-diene using hot concentrated acidified $\ce{KMnO4}$ solution?

Do we approach this problem the same way we would approach oxidation of alkenes?

I'm unsure how this mechanism would work.


texts:
I was reviewing first posts here, and eating a juicy and salty (table salt) tomato at the same time. Suddenly, I realized that a few table salt crystals have been poured down on my mousepad.

I got curious and I rotated the laptop $90°$. I witnessed that the salt is somehow resisting to fall! Not sticked (very firmly attached) though, and the mousepad wasn't wet and didn't contain any possible chemicals that could cause the "attaching";

except that apparently the mousepad is "soaked" with the sebum produced by the tip of my fingers. Sebum, however, is a mixture of non-polar lipids such as fatty acids, triglycerides, sterols, sterol esters, wax esters and squalene. (See here also)

There can be another reason which lies in the electrical field that my laptop produces, and this could affect a compound like table salt that is primarily ionic. (No clue how, am I missing an easy chemistry concept?)

So, is there any possible "mild" (as in invisible) reaction, either chemical or physical, as a reason of the phenomenon? Or is this behavior because of the composition of table salt?

Note that I'm certain about the existence of such thing, though research showed nothing relevant in the Net.


texts: Are we technically reducing electrodes/wires for the instant that an electron passes through them?

texts:
In lecture I was taught that, in a galvanic cell at standard conditions, platinum is often used as an inert electrode when the species being oxidized or reduced exists only in solution, because platinum is "inert," which means it is very stable at its oxidation state and resists reduction or oxidation. This concept confuses me, because "Reduction" means to lose charge, a.k.a. gain an electron(s). When the electrode has an electron passing through it in order to be transferred to another material, isn't it being reduced, albeit for a very miniscule amount of time?
For example, consider a galvanic cell with platinum electrodes and an iron wire. If we were to examine the cell at an instant and examine the platinum electrodes/wire, we would see a charge of -1 on some of the platinum atoms and iron wire, correct?
What I'd like to imagine is that, while platinum is capable of having a negative charge because of the room for electrons in its d-block, the species being reduced in the half-cell will always have a higher affinity for accepting the electron due to its higher standard reduction potential. This still leaves me confused on why platinum is willing to accept the electron and thus making platinum a medium for electron transfer in the first place, though. This all applies to the iron wire (or any other element that may be used for electron transfer) as well, but I would like to tackle the case of platinum overall.


texts:
How do non-sublimable solids exist in equilibrium with vapour?

All substances exist in equilibrium with their vapour, something I learned from Jan's comment. But my question is how does that happen with solids that are non-sublimable, like ice, piece of iron, or, a piece of cotton?


texts: Is there a literature value for the activation energy for the reaction between sodium metabisulfite and potassium iodate

texts: I am doing an experiment where I perform an iodine clock reaction between sodium metabisulfite and potassium iodate. I have an experimental value for this reaction but I need a theoretical literature value to compare this value to calculate discrepancy.


texts: Why is edta in its calcium complex still a tetraanion at pH 10?

texts:
$\ce{edta}$ has different forms according to the pH. For example if the pH is $7{-}10$, $\ce{HY^3-}$, whereas if the pH is $11{-}14$ its form is $\ce{Y^4-}$.

But I've come across an exercise where it says that we titrate $\ce{CaCl2}$ with $\ce{edta}$ and the pH is $13$, and then we titrate it again with $\ce{edta}$ but the pH now is $10$.

The reactions that are given are the following:

$$\ce{CaCl2 + Na2H2Y <=>  Na2[CaY] + 2HCl}$$

Why is the $\ce{edta}$ given as $\ce{Na2H2Y}$ both times? Shouldn't its form be different at different pHs?


texts:
I would like to retrieve pricing information for specific chemicals. Is there a centralized resource for this?

Edit: I want to clarify that this type of data is to conduct a techno-economic study. I know that for certain markets there are centralized databases which collect prices, and report price statistics, I was wondering if there is something similar for the chemical industry.


texts: When is Serpeck's process preferred over Bayer's process?

texts:
Both these processes are used in concentration of bauxite.
They use different reagents.

Which is more commonly used (wikipedia says Bayer's) and why?
When is one preferred over the other?
Which is more efficient and why?


texts:
Today I was conducting a redox titration with $\ce{MnO4}$ and unknown amount of $\ce{FeX}$ which through qualitative observation looked like $\ce{FeO(s)}$. I titrated the $\ce{FeX}$(which was dissolved with 10mL $\ce{H2O}$ and 5mL $\ce{H2SO4}$). I had two questions about this experiment:

1) If I am trying to find the molarity of the unknown $\ce{Fe^2+}$ ions (redox reaction), would the increase in volume (mL) of $\ce{MnO4-}$ increase the yield of $\ce{Fe^2+}$ ?

2) When conducting this experiment I did not rely on any indicators yet relied on the $\ce{KMnO4}$ for colour change. I really don't know what the possible sources of error for this experiment are. I need some help trying to come up with 2.


texts: How can I get this glass stopper out? Need troubleshooting!

texts:
I placed a glass stopper in a $\pu{100 mL}$ round bottom flask while my solution was still warm and let it cool overnight. Now I think I created a vacuum seal and I can’t force the stopper out to filter my product. I’ve tried heating it up again but to no avail. I don’t want to slip oil in there and risk getting it in.

Anyone have a good idea?


texts: Determining Kc for the equilibrium involving iron thiocyanate using spectrophotometric data

texts:
$$\ce{Fe^3+(aq) + SCN-(aq) <=> [Fe(SCN)]^2+(aq)}$$
$\pu{12.0 mL}$ of $\pu{0.00110 mol L-1}$ $\ce{Fe^3+}$ was added to $\pu{6.00 mL}$ of $\pu{0.00140 mol L-1}$ $\ce{SCN-}$. The absorbance of the resulting solution was $0.625$. If the constant $(\varepsilon b) = \pu{3800 (mol L-1)-1}$, determine the value of $K_c$ that should be reported for the equilibrium.
a. $\pu{1.64e-4}$
b. $\pu{3.03e-4}$
c. $\pu{4.67e-4}$
d. $\pu{5.69e-4}$
e. $957$

Answer given: e.
Given what I know about $K_c$ it should be:
$$K_c = \frac{\left[\ce{[Fe(SCN)]^2+}\right]}{[\ce{Fe^3+}][\ce{SCN-}]}$$
which gives me the answer a. I tried calculating $C$ by manipulating Beer's law, but I still don't end up with $957$ no matter what I try.
I would appreciate it if someone could walk me through the steps of solving this problem.


texts: Assigning Cahn-Ingold-Prelog priority numbering rules for 2 groups

texts:
I was asked to draw the perspective formula of

  $$\ce{(3R,4R)CH2=CH-CH(CH3)-CH(CH3)-CH2-CH3}$$

Then I had to assign priority between the two groups:

  $$\ce{-CH=CH2}$$
  and
  $$\ce{-CH(CH3)-CH2-CH3}$$

Actually, they are bonded to the same atoms until the end of the first group, but one of them should have priority over the other.
Can please someone help?


texts: Why "initial" corrosion studies only, rather than longer time-spans?

texts:
Some papers say they study the identification and quantification
of species involved in initial atmospheric corrosion. Consider the case of this article in Corrosion - The Journal of Science and Engineering, for example, it provides an exceptionally good model, but I am interested in the copper corrosion process as a whole, not just the beginning. What exactly is understood as "initial corrosion" and what's the relevance of studying such a short time-span? That paper's tests reach no longer than 300 minutes, while other studies measure time in weeks, not minutes.


texts: Can precipitation reactions attain equilibrium?

texts:
While studying about the characteristics of Chemical Equilibrium, I came across a point in my book which read

A chemical equilibrium can be established only if none of the products is allowed to escape out or separate out as a solid (precipitate)

I understand that if one of the products is a gas and escapes out the reaction won't be able to proceed in the backward direction since that gas is no more a part of the system.
But what I'm not able to get is why it's written that precipitation reactions can't attain equilibrium.
Is there no precipitation reaction which can attain equilibrium?
Or is it that the precipitate can't react back chemically with the solution to produce the reactants in reverse?
My teacher told me about about a reaction
$$\ce{Ca(HCO3)2(aq) + heat -> CaCO3 +CO2 +H2O}$$
and on cooling the solution and bubbling $CO_2(g)$ through it the $CaCO_3(ppt.)$ reacts back to form calcium bi-carbonate.
I'm still a bit confused as the reverse reaction doesn't happen spontaneously. Moreover if the reaction is carried out in a closed vessel and constant temperature (after heating), will the reaction reach equilibrium?
edit
in the answer recently provided, the solid-solution equilibrium between $\ce{AgCl}$ and $ \ce{Ag+}$ $\ce{Cl-}$ ions is discussed. But I want to know if in a reaction like $$\ce{AgNO3(aq) + NaCl(aq)\to AgCl(s,ppt) + NaNO3(aq)}$$
the precipitate $\ce{AgCl(s,ppt)}$ can react with $\ce{NaNO3(aq)}$ in the solution to give the reactants?
Can it reach chemical equilibrium?
I've seen this and this but couldn't understand.
Any of your help is of great value to me.


texts: Do the letters ol in a substance only indicate that the substance is an alcohol if they came at the end of the name of a substance?

texts: Do the letters ol if they are together only indicate the substance is an alcohol if they come together at the end of the name of a substance? for example,is glycerol an alcohol because the letters o and l come together at the end of its name and olives and olive oil are not alcohols because the letters o and l do not come together at the end of any words in their names?


texts: What solute should I use with dialysis tubing if I want a 100% retention rate?

texts:
I purchased dialysis tubing from the Carolina company.

The molecular cut off is 12,000-14,000 Daltons and I've been using table sugar for my experiments with it to raise columns of water. While the sugar does work it slowly leaks out of the membrane over time if it's left to sit for an hour or so. What should I use if I want near 100% of the solute to stay within the dialysis tubing? Preferably something cheap and non-toxic that will also dissolve in water. Or maybe a different type of membrane I could purchase that would retain the sugar better?


texts: Is associative ligand exchange possible with octahedral complexes?

texts:
Can associative ligand exchange produce an octahedral intermediate as long as the initial complex has 16 electrons (unsaturated)?

Not sure. all I ever see is a square planar turning into a trigonal bipyramidal intermediate?


texts: Non polar molecular and attractive forces

texts:
How come when a non polar molecule increases in size, the attractive forces between the molecules of a substance also increase?

I thought that when a molecule increases in size, the atomic radius increases, which creates a bigger space between particles; thus, the force of attraction would be weaker.

But, why does the force of attraction increase when a non polar molecule increases in size?


texts: What defines matter's phase at room temperature?

texts: So, a simple question: what makes neon a gas; what makes water liquid; what makes plutonium-238 a solid at room temperature? Of course, the phase is determined by the excitation of the molecules, but what determines that excitation?


texts:
What are the concentrations of $\ce{Cl-}$ in the following solution? $1.9\ \mathrm{g}\ \ce{MgCl2}$ is dissolved in water to make $1\ \mathrm{L}$ total solution

$$48.31\ \mathrm{g/mol}\ \ce{MgCl2}$$

$$(1.9~\mathrm{g}\ \ce{MgCl2})(1\ \mathrm{mol}/48.31\ \mathrm{g}) = 3.932\times 10^{-2}\ \mathrm{mol}\ \ce{MgCl2}$$

$$\ce{MgCl2 -> Mg+ + Cl2-}$$

$$(3.932\times 10^{-2}\ \mathrm{mol}\ \ce{MgCl2})((1\ \mathrm{mol}\ \ce{Cl2})/(1\ \mathrm{mol}\ \ce{MgCl2})) = 3.932\times 10^{-2}\ \mathrm{mol}\ \ce{Cl2-}$$

then

$$(3.932\times 10^{-2}\ \mathrm{mol}\ \ce{Cl2-})/(1~\mathrm{L}) = 3.932\times 10^{-2}\ \mathrm{M}\ \ce{Cl2-}$$

Is that correct? Or does the $2$ go infront of the $\ce{Cl}$, so the mole ratio is $((2\ \mathrm{mol}\ \ce{Cl-})/(1\ \mathrm{mol}\ \ce{MgCl2}))$?


texts: Why do we need to assume that gas is made up of large number of small particles in kinetic molecular theory of gases?

texts:
Among the five postulates or assumptions of kinetic molecular theory of gases (KMT), only the assumption that a gas is made up of large number of small particles doesn't seem to make any sense to me. The only reason I could of think of was due to lack of negligible pressure. I reasoned that if there aren't enough molecules in the container there will be no evidence of pressure, since most of collision would be within molecules and not between the wall of the container and the molecules. But there is something missing in this explanation or it is completely wrong, as it fails to adequately explain the above stated question.
Why do we need this assumption?


texts:
The beryllium iodide $\ce{BeI2}$ as covalent compound is apolar, and thus, it should be water non-soluble. However, it is. Making a research on the web, I learned it is just in the middle of being ionic. Dos it happen with the $\ce{MgI2}$ of $\ce{MgF2}$ as well? I usually explain the following to my students:

Solubitity "general" rule: "Similar dissolves similar".
Solubitity is also affected by differences in electronegativity and bonding polarity.
Solubility is also affected by the capability to displace charge and solvation (that is, intermolecular forces also apply to some extent).
As a practical rule, we can consider ionic compounds those formed by G1 or G2 with G16 or G17, but this rule has exceptions, like the rules of electronic configurations.

Is all stuff correct? Solubility in water of $\ce{BeH2}$ and $\ce{XeF2}$ can be also considered with these rules?


texts: I know that the proton will attack the HOMO, but I'm having difficulty imagining how this will happen.


texts: Associated occupation numbers of frozen natural orbitals (FNOs) from MP2 method

texts:
The paper Frozen Virtual Natural Orbitals for Coupled-Cluster Linear-Response Theory gives the following (simplified) description of frozen natural orbitals (FNOs).

In the MP2 method, the unrelaxed one-electron density matrix can be written in terms of spin orbitals

$\gamma_{pq}=\langle\Psi^{1}|\{a_{p}^{\dagger}a_{q}\}|\Psi^{1}\rangle$

where $|\Psi^{1}\rangle$ is the first-order correction to the Hartree-Fock wavefunction.
In the MP2 based NO method, the virtual-virtual block is constructed:

$\gamma_{ab}=\frac{1}{2}\sum t_{ij}^{ac}t_{ij}^{bc}$

and then diagonalised:

$\gamma V=nV$

The eigenvectors V are the virtual NOs, and the eigenvalues n are the associated occupation numbers.

If the eigenvalues are found from a virtual-virtual (unoccupied-unoccupied) block, how can there be an associated occupation number?


texts: Why is the probability of a didentate ligand to form a chelate with a central atom, high?

texts: When one ligating group of didentate ligands (like ethylenediamine) is coordinated with a central atom, then the probability of the other ligating group being coordinated, and hence forming a chelate, is high. This is seems to be because one of the ligating groups is bound to be closer to the central atom when the other is coordinated. Does this always hold true? If so, why?


texts: How long can iodine bottle left open? Can it go bad sooner than expiration date?

texts:
I have bought iodine about a year ago but the bottle cap got damaged during the transportation and it leaked all over the package, but I have decided to keep it anyway. Unfortunately I did not use it to anything and it was just sitting on my shelf with cracked cap with about a one millimetre sized hole.
I wonder if it could go wrong and now it's useless. As far the expiration date, it's still not expired, but that's probably when the bottle is fully sealed.
So is it still safe to use if needed or I can return it to the drug store so they can safely dispose it?
Content for 100ml: iodopolyvidonum 7,5g with 10% content of Povidone-iodine (M.h. 40 000)
Thank you


texts: what happens to the intramolecular bonds within water molecule during phase changes?

texts: Does intramolecular bonds within water molecule change during phase changes?


texts: What (non toxic) light sensitive materials do not burn away at high heat?

texts:
Specifically related to photoceramics, I am wondering what photosensitive materials exist that can be bonded to glass at high heat in a kiln (a microwave kiln to be more exact).
By non-toxic I mean a material that does no give off hazardous fumes, so silver, cyanotype and dichromates would be out of the question as far as I am aware.
The process I had in mind is, coat on glass, expose image via contact print using UV, then kiln fire to make the image permanent with the glass.
If there exists a photosensitive glaze out there, I would love to know!


texts: Mechanism of protein precipitation with TCA

texts:
In practice, TCA (trichloroacetic acid) is widely used for quantitative protein precipitation, but so far I have failed to discover the exact mechanism of TCA action. I highly doubt it's just the effect of pH that precipitates proteins.
Any better guesses?


texts: Why is the change in enthalpy computation for a change of state done like this?

texts: Suppose that a system whose initial state is Pressure = $P_1$, Volume = $V_1$; and it is taken through a process after which final pressure and volume are $P_2$ and $V_2$ respectively. Now change in enthalpy is defined as $\Delta H= \Delta U +P\Delta V+V\Delta P$The thing which I am confused with is which pressure and which volume do we hold constant for their respective parts in the calculation? Till now I had dealt only with problems involving the $P\Delta V$ part, and it was calculated as $P_2(V_2-V_1)$, same as irreversible work. But when I came across a problem in which Pressure also varied with volume, the second part needed to be taken as $V_1(P_2-P_1)$.Why do we take $P_2$ as constant in one case and $V_1$ in the other?One reason which I thought of was that in an irreversible process, The pressure is first changed by a finite amount and then the volume varies. Thus the pressure throughout the process was $P_2$. This can be a rationale for the $P\Delta V$ part, but I am not sure if it is reasonable to say that the volume at start of the process was $V_1$, which resulted in this method of calculation. So.. what is the reason?


texts:
why does SiO2 form a crystal structure while CO2 forms a linear one? Would it be possible to make a CO2 crystal or SiO2 gas in a lab or is there something preventing that from happening.

Thanks


texts:
My professor says that $\ce{Li}$ and $\ce{Na}$ are produced by electrolysis, while $\ce{K, Rb}$, and $\ce{Cs}$ are made via the reaction $\ce{Na + MCl -> NaCl + M}$, where $\ce{M = K, Cs, Rb}$.

I don't understand how the reaction $\ce{Na + MCl -> NaCl + M}$ can take place, given the reduction potentials of the alkali metals ($-3.04, -2.71, -2.93, -2.98,$ and $-3.03$ V for $\ce{Li, Na, K, Rb, Cs},$ respectively). From the data, we see that sodium is the weakest reducing agent and the least electrochemically active among these alkali metals. Why then, would it prefer to displace a more electrochemically active species?


texts: Would graphite stick to basalt cooled from its molten state in a graphite mold?

texts:
Molten metal that is poured into a graphite mold pops out easily once it has cooled. Would basalt poured the same way pop out just as easily?

I am particularly interested in lunar basalt, if that makes any difference. The image shows the composition used to make a lunar regolith simulant, taken from chapter 13 of Resources of Near Earth Space, by B. J. Pletka.


texts: Resources to learn computational chemistry?

texts:
I am interested in learning computational chemistry to explore the possibility of postgraduate work in quantum/theoretical chemistry and would like to attempt self-studying.  I know the basics of quantum mechanics on par with a p.chem course and have an understanding of linear algebra and differential equations.  Are there any other resources that would help me in learning?

As far as I know, there is no software suited for learning computational chemistry on a desktop PC.  But would there be anything similar that would assist in my learning?

Also I am lacking in the programming side of things, would that be a significant barrier to my learning, especially when using computational software in the future?


texts: In the Wittig reaction, why do stabilised ylides produce E-alkenes and unstabilised ylides produce Z-alkenes?

texts:
Wikipedia says that with unstabilised ylides they react very quickly in step 1-2 and step 4-5 is the rate limiting step. But with stabilised ylides step 1-2 is the rate limiting step and this is why stabilised ylides give E-alkenes. But there is no explanation as to why this makes E-alkenes and where in the mechanism it occurs.

I would have thought stabilised and unstabilised ylides would give E-alkenes to reduce steric hinderance but this is not the case. Any help explaining this would be very appreciated. :)


texts: Entropy of universe for non spontaneous processes

texts: When spontaneous processes are accompanied with an increase in entropy of universe and remains unchanged in a reversible process, what happens to entropy when one process is non spontaneous? Would entropy decrease??


texts: Does this electronic configuration violate the Hund's rule of maximum multiplicity?

texts: I know this configuration violates the AufBau principal but does it also violate Hund's rule of maximum multiplicity?


texts: Sodium Perborate as a detergent ingredient

texts: Sodium Perborate is a well known bleaching agent in detergents. What makes Sodium Perborate an effective bleaching agent and how is this related to its oxidation chemistry?


texts: What is the derivation of the formula for finding number of pure and hybrid orbital?

texts:
I am studying Organic Chemistry. Recently I came up with the formula for finding number of pure and hybrid orbital that can be present in a organic compound. That is:

Number of Hybrid  Orbital = number of "Carbons" $\times$  (number denoting the hybridisation of carbon) and
Number of Pure Orbital = number of Hydrogens present $+ 2 \times$  (no of $\pi$-orbitals present)

Example Benzene:

number of hybrid orbital $= 6\times (3) = 18$ (Hybridisation is $\mathrm{sp^2} = \mathrm{1s} + \mathrm{2p} = 3$)
number of pure orbital $= 6 + 2 \times 3 = 12$

which tells that there are 18 hybrid orbitals and 12 pure orbitals present in benzene.
My question is, What is the derivation of this formula?


texts: RCSB PDB - how to choose between multiple copies of the same protein?

texts:
I want to map the location of missense mutations on a protein, SERPINB3. I intend to do this using PyMol and download the protein structure from RCSB PDB. However, searching for SERPINB3 reveals two molecular structures (as well as one homolog, SERPINB4).

One of the structures, 2zv6, presents the protein as a multimer of three identical chains. This structure is older (2009) and is used by computational tools on CbioPortal.

Another structure, 4zk3, presents the protein as monomer and has been more recently published (2015).

I am inclined to trust the more recent protein over the older one on the vague notions that:

Its newer so it was probably an improvement in terms of some aspect of the structural determination process
I've heard that its "unusual" for a multimer to form with three identical chains

...which are not particularly good rationalizations.

I have not found any literature comparing these competing molecular structures and honestly I am not entirely clear on how different they are from each other beyond the fact that one is presented as a multimer.

What justifications can be made based on chemistry and/or biology to support one of these structures over the other? I am interested in both choosing between these two structures and in general good practices for choosing between two competing structures.


texts:
Following up on the question Units of mass on the atomic scale,
Daltons (Da) and unified mass units (u) are equivalent, but which is used seems to depend on context.  For example, when discussing single atoms one typically sees the mass expressed as u, but when discussing large biomolecules one typically sees Da or kDa.

Is there a rule about whether to use Da or u? Or, is this simply a matter of convention or left to the writer's choice?


texts: What does the number of orbitals in a subshell represent?

texts: s subshell has 1 orbital and p subshell has 3 orbitals. Does that mean that there is a high probability that the electron is in the p subshell? As orbital are the space where there is a high probability of finding electrons.


texts: 18 Electron Rule For Determining the Stability of Transition Metal Complexes

texts:
I chanced upon this 'rule' while I was messing around on Wikipedia, and since we just finished studying about transition metal complexes at school, it naturally drew my interest.

Though I did read the article on it on Wikipedia, I don't feel I've really grasped the concept well enough (in short … I'm kinda lost).

So I hope it isn't too much to ask but, is there someone here who's willing to spend some explaining the 18 electron rule, lucidly enough for a 17 year old to understand? Or if that isn't possible, could someone recommend a site that explains the rule decently enough? Also could you touch upon some exceptions to the rule (at least for period 4 transition metals)?


texts: Which software is suitable to calculate the root mean square deviation between two protein structures?

texts: I need to compute the root mean square deviation (RMSD) between two protein structures: the X-ray determined protein structure and the MOPAC optimized structure. Which software do you suggest?


texts: I see the suffix "sine" (seen/sin) a lot, adenosine, cytosine, lysine, tyrosine, etc. Most of where I hear it is in amino acid R groups, but it's usually only the prefix that is recognized as significant.


texts: Best Radioactive Isotopes for Energy Generation

texts:
First off, this is research for a video game storyline, I like to be thorough.

--

I am looking for the most efficient method of nuclear power generation which:

Can survive for hundreds/thousands of years (a no-brainer for isotopes)
Has some kind of non (or minimally) radioactive decay product/by-product.

The storyline is based in the 2050's, so I can use a little poetic license, I just want to get things as close to reality as possible.

This would be used to power a large city and scientific research base, for which several generators could be used, but I was wondering on which material would be best to generate such power consistently.

These facilities have consistent access to clean, flowing water so heavy water theoretically could be used in the energy generating process.

I started looking at our currently used isotopes, $\ce{^{234}U}$ and others, but I am looking for a material that would be compatible with both fusion and (what would then be legacy) fission (if possible).

$\ce{^{232}Th}$ seems like a promising start, but I thought I should ask before basing everything on extremely flawed science.

Any suggestions?


texts: Double Replacement Reactions form Precipitates

texts: Why do most all double replacement reactions result in a precipitate and an aqueous molecule? Is it because the individual solute molecules always form stronger bonds such as how in single replacement the molecule with more energy bonds with the molecule of the opposite charge?


texts: Determining priority for a cyclic compound

texts:
I have problem in determining the CIP priorities in (S)-ketamine.

What is the order of priorities for esketamine? Does the carbon bonded to the ring with chlorine have higher priority compared to the carbon bonded to oxygen?


texts:
According to this paper, isoindole is unstable because the 1-carbon in the isoindolidine tautomer is very electron-deficient.  I figured that the electron-deficiency of this carbon must be because it is bonded to an aromatic carbon and double bonded to a nitrogen, both of which atoms are electron-withdrawing.

By this logic, I would expect other carbons in this situation (C(aryl)-C=N) to also be very electron-deficient.  However, aromatic Schiff bases seem pretty common, for example salen.  What am I missing?


texts: Determining the calcium content in cashews via titration?

texts:
I have been planning on an experiment for quite some time now (as part of my after-school chemistry club), but I still feel like I am missing something.

Due to my family's calcium deficiency, I decided to measure calcium content in various foods. It's something rather personal, therefore it will make the experiment more interesting overall.

At first I wanted to choose dietary supplements since they can dissolve easily, though then I realised how flawed of an idea that is, since the contents are usually given on the package in full detail anyway. In then moved onto fruit and other various foods, though it all seemed rather messy/ hard to achieve.

I then realised I could measure the calcium content in cashews. I was thinking about using EDTA and Eriochrome Black T, as well as methyl orange. Here is where I hit my first struggle - how do I dissolve the nuts in the first place? I thought about acids, such as hydrochloric acid, though that would as a result affect the pH of the solution (which, I am not sure, could have an effect on the way the titration procedure functions).

I'd use methyl orange together with Eriochrome as the transition is much clearer since it goes green then grey, whereas the transition from purple to blue is rather subtle - in my opinion this would increase the accuracy of my experiment.

Alternatively, I could use absorbance technique to determine the calcium content - would it be more appropriate for this scenario? I could use a stock solution to find for example the absorbance of 10ppm before calculating the absorbance of the cashew. Does this sound more appropriate?

Any input would be greatly appreciated!
These can be hints, I definitely want to work through the issue myself as much as possible. I just seem to be stuck and don't know where to go from there!