texts: Why do some elements with high electronegativity exhibit metallic properties?

texts: Metals typically have low electronegativity, which makes them form ions easily and prefer making metallic bonds to covalent. However, some of them seem to disprove that. Take, for example, gold, lead and phosphorus (for comparison). Their electronegativity values are 2.54, 2.33 and 2.19 respectively. Phosphorus is a typical non-metal, while gold and lead should have higher electron affinity and be even stronger non-metals that phosphorus. Why isn't that true?


texts: Why "RCA clean" solution has to be prepared every time (and not stored long-term)?

texts:
"RCA clean" solution is a 5:1:1 mixture of DI water, ammonium hydroxide and hydrogen peroxide.

Why the ready 5:1:1 solution is not stored for long term, but instead has to be prepared each time immediately prior to usage?


texts:
I am looking for methods to determine the dissociation free energy in a precise way, ideally from a simulations. My hope is to get the most precise values possible that are specific to the structure of the chemical element, rather than the more general energies I have found that completely ignore the context of the molecule (like in "Bond Dissociation Energies of Organic Molecules", ACCOUNTS OF CHEMICAL RESEARCH 2003). A machine learning program that can assess the bond energy of an input molecule using parameters learned from a database would be ideal.

Alternatively, I would like to know what are the most accurate and reliable source for such values, as I have been having trouble finding sourced values.

The goal is to use these values to calibrate other properties of a system based on thermodynamic cycles. Since this calibration is for molecular simulations, I need accuracy but most importantly, consistency between methods. I can live with not so accurate parameters, as long as the overall force field is balanced, meaning the differences are balanced.


texts: Why don't Gringard Reagents react with carbonyls at the alpha position?

texts:
According to many texts, the reason why Gringard reagents cannot be used with alcohols is because the Gringard reagent is a strong base, which would deprotonate the alcohol. ($p\pu{K}_b$ of Gringard $\approx 50$).

However, carbonyls also have a fairly acidic hydrogen at the alpha position ($p\pu{K}_a$ of enol $\approx 20$), so why does the Gringard reaction react with the electrophilic carbon, rather than as an acid-base reaction with the alpha position to form an enolate?


texts: Can H– act as a strong Brønsted base like CH3–?

texts: In the reduction of carboxylic acids with $\ce {LiAlH_4}$ we get an alcohol. But isn't there a possibility of the hydride donor abstracting $\ce {H^{+}}$ from the acid to form $\ce {H_2}$?


texts: Determining amount (in mols) of oxygen needed to fully combust coal

texts:
I'm trying to calculate the amount of oxygen needed to fully combust some coal.

As an example, assume I have $\pu{1 kg}$ of coal which is, by mass fraction, 60% carbon ($\ce{C}$) 40% hydrogen ($\ce{H}$). I know this is unrealistic but it's just for the sake of the example.

There is then $\pu{0.6 kg}$ of $\ce{C}$ and $\pu{0.4 kg}$ of $\ce{H}$. I can convert to $\pu{mol}$ by using the MW of both species, $\pu{0.012 kg/mol}$ for $\ce{C}$ and $\pu{0.001 kg/mol}$ for $\ce{H}$. Which means I have $\pu{50 mol}$ of $\ce{C}$ and $\pu{400 mol}$ of $\ce{H}$.

The reaction stoic for the oxidation of both species is as follows:

$\ce{C + O2 -> CO2}$

$\ce{4H + O2 -> 2H2O}$

Would it then be correct to say that I need $\pu{100 mol}$ of $\ce{O2}$ to combust the $\ce{H}$ and $\pu{50 mol}$ of $\ce{O2}$ to combust the $\ce{C}$?


texts: net charge nucleobases at alkaline conditions

texts:
While doing anion exchange chromatography of a short oligonucleotide, I have noticed that at $\rm pH=12$, the oligo retains longer on the column than the same oligo- at $\rm pH=8$. I thought the reason for this could be the change in the net charge of nucleobases.

Could anyone suggest what is the net charge of RNA nucleobases (adenine, guanine, cytosine, uracil) at $\rm pH=12$ (denaturing conditions)?


texts: How to measure amount of oxygen (or carbon dioxide) in air?

texts:
I'm not chemist, and I'm looking for easiest way to measure how much oxygen plant in closed container will produce per hour [can measure over time for increased accuracy].

My first idea was to measure percentage of oxygen in air with automotive lambda sensor.

However I don't expect good precision of measurement like this, and this is a little complicated (lambda sensor needs high temperature, so I need to heat it up).

I wonder if there is some chemical way to perform measurement like this.


texts: Chemically removing rust without leaving any unwanted residues

texts:
I have this iron pan that got rusty from not being properly dried. Scrubbing it I was able to get rid of most of the rust, but there's still some I just can't remove. I thought I could chemically remove it, but I myself am a bit rusty on the inorganic chemistry subject, so I couldn't think of any way of doing it without leaving any unwanted residue on the pan.

The rust is the brownish-red type, which according to Wikipedia consists of $\ce {Fe2O3·nH2O}$ and $\ce{FeO(OH)·Fe(OH)3}$. Most rust-removal "recipes" I found involve all sorts of acids, but I can't tell what the reaction(s) would be with $\ce {Fe2O3·nH2O}$ so I can't tell if there would be any residues left behind that I could not remove. Anyone with any experience on the matter?

I contacted the manufacturer and the pan is hand-made, just Iron and natural coating (fat).


texts: Given volume of reagents find the chemical formula of nitrogen oxide

texts:
$$\ce{NH3 + O2 -> N_xO_y + H2O}$$

I know that there is $\pu{1 m^3}$ of both the nitrogen oxide and the ammonia and the volume of oxygen on the left side is $\pu{1.25 m^3}$.

I think that I should use the ideal gas equation. It is also obvious that there is only one atom of nitrogen in the oxide - I guess that there is also only one oxygen.

Could anyone give me any hints?


texts:
I recently took a chemistry test in which the following problem was offered:

a 137 mL gas sample is collected over $\ce{H2O}$ at $753\ \mathrm{mmHg}$ and $22\ \mathrm{^\circ C}$. What is the volume of the dry gas at STP if the vapor pressure of $\ce{H2O}$ at $22\ \mathrm{^\circ C}$ is $22\ \mathrm{mmHg}$?
a) $106\ \mathrm{ml}$
b) $117\ \mathrm{ml}$
c) $123\ \mathrm{ml}$
d) $126\ \mathrm{ml}$

Here's my work:
To start with, I used Dalton's Law of partial pressures:
$$p_\text{total}=p_\text{gas}+p_{\ce{H2O}}$$
$$p_\text{gas}=731\ \mathrm{mmHg}\ \left(\text{at}\ 22\ \mathrm{^\circ C}\right)$$
Then I used the following proportion to find the volume of the gas:
$$\frac{p_\text{gas}}{p_\text{total}}=\frac{V_\text{gas}}{V_\text{total}}$$
$$V_\text{gas}=133\ \mathrm{ml}\ \left(\text{at}\ \mathrm{^\circ C}\right)$$
Which made sense to me because if the total number of moles of the gas mixture is not changing, and the temperature is not changing the ratio of the volumes should be the same as that of the pressures (shouldn't it?)
Finally I did a bit of dimensional analysis to change from $22\ \mathrm{^\circ C}$ to STP:
$$133\ \mathrm{ml}\ \cdot\ \frac{731\ \mathrm{mmHg}}{760\ \mathrm{mmHg}}\ \cdot\ \frac{273\ \mathrm K}{295\ \mathrm K}$$
$$V_\text{gas}=118\ \mathrm{ml}\ \left(\text{at STP}\right)$$
I feel like I'm missing/forgetting a key concept here because each individual step made sense in my head (and still makes sense now). The answer the prof gave was d. This is bugging me a lot and I would appreciate any help.


texts:
Considering the Arrhenius theory of acids and bases:

Is every existing compound either an acid or a base?
Why is a compound such as $ \ce {NH_3}$ considered a base, if it doesn't even have an oxygen atom and a base is supposed to release $ \ce {OH-}$ in water?
If $X$ is a base according to Arrhenius theory, will $X$ still be a base according to the other two theories (and the same if $X$ were an acid)?

According to the Brønsted-Lowry theory:

There are no absolute acid and bases, but only acid-base reaction in which one compound acts as a base and the other as an acid. So, is every reaction of two compounds an acid-base one?
Except for water, are there any other substances which in some reactions act as bases while in others as acids?


texts: Why do neutron scattering lengths vary seemingly randomly with atomic number?

texts: I'm a bit unclear as to what determines neutron scattering lengths, and hence why they can vary so much even between adjacent elements like Fe and Co. I gather it's related to resonant scattering, but I would be very grateful for an account (ideally not purely mathematical!) of how and why.


texts: Magnesium Sulfate (MgSO4) back to Magnesium Oxide (MgO) + Sulfuric Acid (H2SO4)?

texts:
Is it possible to go back from magnesium sulfate ($\ce{MgSO4}$) to magnesium oxide ($\ce{MgO}$) and sulfuric acid ($\ce{H2SO4}$) ?

How difficult or easy would it be?

The reason I ask is because epsom salts ($\ce{MgSO4}$) are really cheap (i.e. less than 50 euro cents / kg). Whereas magnesia ($\ce{MgO}$) of $98\%$ or better grade is much more expensive (i.e 3-4 euro / kg).

I was wondering how easy and cheap it would be to revert the reaction and separate out the sulfur from the magnesium oxide.


texts: I am told that an intramolecular proton abstraction can occur. For some reason this seems at least sterically unlikely. Is it possible sterically? Or is the proton abstraction best described as a equilibrium process between the nitrogen's hydrogens and water?


texts: Do lithium batteries 'explode'/'burn' because of the electric energy stored within?

texts:
I've been watching some videos where people show lithium ion batteries burning/exploding. What usually happens is someone punctures the battery, and a jet of gas comes out the puncture hole, followed by the gas catching fire and the entire thing going up in flames.

I often hear that the energy for this reaction comes from the chemical energy stored in the battery. Thing is; i'm pretty sure that there wouldn't be enough chemical energy in the battery to cause such an intense reaction. I'm thinking that it's probably the lithium inside the battery reacting with the air in an exothermic manner.

So what exactly causes the reaction that we see? Does it have anything to do with the electric energy stored in the battery or is it just a lithium/oxygen reaction?

Edit: It was suggested I actually do the math. So here goes; typical energy density of a lithium ion battery would be around 200 watt-hours per kg of battery mass. Therefore a 1kg battery would have about 720 kJ of chemical energy. Proceeding from here we would need to know at the very least a.) the mass of the substance we see being 'exploded', b.) the specific heat capacity of said substance.

For example; if I assume that from a 1kg battery we'd have 300 grams of material being heated up and expelled from the battery, and that said material has a specific heat capacity of 2 kJ/(kg K) , and that said material starts at 293 kelvin, then I'd know that it would take .6 kJ of energy to heat said material up by 1 degree Kelvin. 720 kJ would be enough to heat it up to 1493 Kelvin, assuming 100% of the energy went into heating up just that 300 grams of material and not the other 700 grams. With a specific heat capacity of 3kj/(kg*kelvin) we'd get a temperature of 1013 Kelvin.

I suppose it'd really come down to what the substance we see shooting out of the battery is, and how much is shooting out of the battery, and what it's heat capacity is (and whether it's approximately constant across the temperature range of interest).


texts: How to make standard sample for NMR signal-to-noise ratio

texts:
I want to make a sample for proton NMR signal-to-noise-ratio measurement. It is conventional to use 1% ethylbenzene in d-chloroform, as specified here.
I have two questions:

What is meant exactly, by 1% ethylbenzene? In some places, I see the notation (v/v), which I take to mean 1% by volume. However, I am still not clear what this means. Does it mean that an amount of ethylbenzene should be used that would fill 1% of the final volume when the solvent is not present? Or does it mean to fill 99% of the final volume with the solvent and then add ethylbenzene until I reach the total volume? Or something else?

What is a good procedure for making such a solution? I imagine a volumetric flask would be useful, but should the solute be measured out by weight? Or using a pipette? I only need about 10 mL of the final solution.


texts: I have read that gases under identical conditions of temperature, pressure, and volume contain the same number of molecules, but every gas has different types of atoms so their force of attraction is also different then how can this be true?


texts:
From the "Technical guide for the elaboration of monographs" by EDQM, edition 7, 2015, page 25:

  Where the counter-ion of an active substance is formed from a lower organic acid, a test for related substances of the organic moiety is usually not considered necessary (for example, magnesium lactate used as a source of magnesium).

What is the meaning of "lower organic acid"? An organic acid of simple composition, with a short alkyl group?


texts:
For which element 'X' is the carbocation $\ce{CH3-X-CH2+}$ the most stable?

A. X = S

B. X = N

C. X = O

I thought since oxygen is the most electronegative among the options, it would create the greatest electron deficiency, which would in turn facilitate a lone pair donation from the O atom (which happens with boron halides), so the answer should be oxygen. However the answer given is nitrogen. I really can't understand why. Is my logic wrong? Or is there more to this question?


texts: Does a zinc metal coating react with coffee in a coffee grinder?

texts:
I'm restoring an old coffee grinder and I want to give the grinder mechanism a nice zinc / silver coating.

But I read it is not safe for zinc to be in contact with acidic foods.

When I look at the pH, coffee's is 4.6 – 4.3 which is quite acidic:
https://angelscup.com/blog/taste/coffee-acidity-flavor-ph-acid-reflux-and-low-acid-coffee/

Not sure if the zinc and coffee are likely to react in such a scenario. Should I maybe choose a silver plating?

Before cleaning with citric acid.

After cleaning with citric acid, Al foil and baking soda


texts: Change of electronegativity of carbon atom by changing substituents

texts:
I was wondering how electronegativity and charge of carbon atom is affected by switching the substituents.
For example what will be the difference in electronegativity of carbon atom in CF3, CCl3, CBr3, and CH3.


texts: Maximum force that hydrogen-hydrogen bond can withstand

texts:
For $\ce{H-H}$:

bond length is $74~\mathrm{pm}$
bond energy is $436~\mathrm{kJ~mol^{-1}}$

(Source: article chemical bond on Wikipedia.)

The University of Waterloo page that the article cites says:

  The amount of energy required to break a bond is called bond
  dissociation energy or simply bond energy.

and

  The bond energy is essentially the average enthalpy change for a gas
  reaction to break all the similar bonds.

So I'm assuming that as the average enthalpy change increases, so does the force that stresses the bond (and thus the forces on each hydrogen atom).

For a single molecule of $\ce{H-H}$, what is the maximum force that the bond can withstand before breaking?


texts: When naming hydrocarbons, when do you number the branch or double bond?

texts: I have realized that not all chains and double bonds are numbered. I have noticed that up until 3 carbons in a chain, the double bond is not numbered, but I am not sure about the chain.


texts: The colour of a complex compound is due to unpaired electrons. As per crystal field theory, $\ce{K4[Fe(CN)6]}$ has no unpaired electrons so it has to be colourless. But then why is it coloured?


texts: I am perparing for a presentation on the application of TiO2 nanotubes in cement which is a recent topic in cement chemistry. Do you happen to have any papers (or know of any accessible on Internet) on the topic from the recent years that you can share with me? Or even if you have any information/experience to share, I would be grateful.


texts: Effective core potential and Gaussian basis set

texts:
Is using the effective core potential (ECP) and Gaussian basis set simultaneously in ab initio calculation a valid approach? For example, is it correct to use ECP for one of the atoms and, instead of a basis set which is optimized for ECP, to take a normal Gaussian basis set (say, 6-31G) when we perform calculations for a molecule with a Hartree–Fock method?
P.S. I know technically I can do it in the quantum chemistry packages (for example, I have checked it in MOLPRO), but I don't know whether it is valid physically.


texts: Mechanism for the conversion of an unsaturated alkyl halide to an alcohol

texts:
Question:

Predict the mechanism for the following reaction:

Attempt:
I thought it will proceed through SN1 mechanism as $\ce{H_2O}$ is involved (solvolysis). So I proceeded with the formation of a primary carbocation, which then rearranges via 1,2 methyl shift. Then the nucleophilic attack of $\ce{OH^{-}}$ leads to the following product, which is different form the required one.
Can any further steps lead to the required product or am I wrong from the start (most probably)?


texts: Is there intramolecular hydrogen bonding in salicylaldehyde?

texts:
Is there intramolecular hydrogen bonding between the hydroxyl and carbonyl groups?

I think personally is that it does but what is concerning me is that I have got no adequate answer or response to my suggestion, so if anyone could help on this one, that would be great.


texts:
I'm having trouble with the following set of reactions and their products.

Product A is achieved by exploiting the unique aromaticity of cycloheptatriene cations. When A  is treated with the Grignard reagent $\ce{MeMgI}$, a mixture of B and C is obtained. Treating A with catalytic amount of $\ce{HCl}$ in $\ce{CCl_4}$ furnishes isomer A’, which is again converted into a mixture of B and C upon treatment with Lewis-acidic Grignard reagents.

For A I got the following structure, since I could not figure out how the aromaticity of the first structure is affecting the reaction.

This cannot be correct, since the grignard reaction would produce only one product and not a mixture of two.

Having done some reasearch online on the resonance structures of cycloheptatriene, I thought of the following structure for A. But this would not produce two different products either if I am not mistaken.


texts: Conversion of Hessian from internal coordinates to cartesian coordinates

texts:
I have performed a CASPT2 frequency calculation using the MOLCAS8 program package. I need the full Cartesian Hessian matrix as input for a subsequent program package.

MOLCAS8 performs CASPT2 frequency calculations numerically. The program MCKINLEY is called for this purpose, however, it is now my opinion that all numerical second derivative calculations in MOLCAS are handled not by MCKINLEY but by the barely documented module supermac. Anyway, the Hessian is fully printed in internal coordinates once the calculation is finished. For a system of 10 atoms the internal Hessian is of size 24 x 24, which suggests non-redundant internal coordinates (MOLCAS calls them "primitive internal coordinates").

Does anyone know of a software capable of transforming a Hessian matrix from internal coordinates to Cartesian coordinates? I am aware that this will probably be complicated as internal coordinates are not as unambiguous and straight-forward as Cartesians. However, my initial search efforts did not yield a single software package capable of transforming a calculated Hessian in internal coordinates to Cartesians. Any help would be appreciated!

Alternatively, does someone know a quantum-chemical program package using which I might be able to obtain a full Cartesian hessian at CASPT2 level?

I don't know if this helps, but MOLCAS also seems to print out the force constants of each atom in Cartesian coordinates. Furthermore a .molden file is produced where the normal modes are included. The full Hessian does not seem to be written to this Molden file though.


texts: Changing Temperature of a Galvanic/Voltaic Cell: Should I wait for the electrodes to also change in temperature?

texts:
I'm conducting an experiment where I change the temperature of the sulfuric acid in a lead acid storage cell. My one question in controlling the variables is that should I let the electrodes also change in temperature, or should I keep them at room temperature and measure the cell potential? Does it even matter at all?

What I'm guessing is that a change in temperature affects the resistance of a metal, which would then affect the ability of the electrodes to transfer the electrons involved; therefore, the electrodes should be kept at room temperature.

If I should do one or the other, could someone explain to me why?


texts:
The book I'm reading writes that for a system at constant pressure and temperature it holds:
$$dG=-TdS_{tot}$$
where $dG=dH-TdS$.
So if you want to see if a certain process is spontaneus, you just have to look at the sign of $dG$, since it depends on the sign of $dS_{tot}$.
But I have a lot of doubts about this formula, indeed read the following scenario.
You consider a certain amount of liquid inside a piston at a fixed pressure given by the weight of the piston. Let's assume the liquid is changing its phase, so also its temperature stays constant at the value $T$. Out there is a heat reservoir at the temperature $T_{res}$, which touches the piston. Since the temperature can't be a discontinous function, you assume that there is a piece of metal which connects the reservoir and the piston. You have:
$$dS_{tot}=dS_{res}+dS+dS_{metal}$$
If you consider a stationary transform, the state of the piece of metal doesn't change, then $dS_{metal}=0$.
$$dS_{tot}=\frac{\delta Q}{T_{r}}-\frac{\delta Q}{T}$$
Since pressure is constant:
$$dS_{tot}=dH[\frac{1}{T_{r}}-\frac{1}{T}] $$
Note that if $T_{r}=T$ then $dS_{tot}=0$ since there are no irreversibility in the universe (no finite differences of temperature), otherwise it must be $dS_{tot}>0$. I would stop at this point but let's introduce the Gibbs free energy.
Definig the Gibbs free energy as:
$$G=H-TS$$
$$dG=dH-dTS-TdS$$
$$dH=dG+dTS+TdS$$
For constant temperature:
$$dH=dG+TdS$$
You finally get:
$$dS_{tot}=(dG+TdS)[\frac{1}{T_{r}}-\frac{1}{T}] $$
Which is not the same thing that writes my book. Also note that the temperature and the pressure of the system are constant, so I have the same hypothesis of the book but I get different results. Someone could clarify this? I'd really appreciate.


texts: Can anyone explain this condensation pattern?

texts:
What is the hair-like polymer that condenses on the caps of the plastic cell vial? Inside vial are cells in a mixture of FBS and DMSO. The vials were frozen slowly in a special isopropanol-filled container (isopropanol does not touch the vials) to $\pu{-80^\circ C}$, then put on dry ice to move to a liquid nitrogen cryogenic freezer.

The hair-like crystals appear to be water, but bend toward my finger when nearby, similar to static attraction. I suspect that it has something to do with DMSO/isopropanol leaking out, and the very low temperatures that cause this strange condensation pattern, but I'm not sure.


texts: Is the term 'hydrophilic' a synonym of 'water soluble' or can you have a molecule that is water insoluble but hydrophilic (or water soluble and not hydrophilic)?


texts: Equivalent mass in case of disproportionation reaction

texts:
I came across a question where the equivalent mass of hypophosphorus acid is to be found in the given reaction:
$$\ce{2H3\overset{+1}{P}O2 -> H3\overset{+5}{P}O4 + \overset{-3}{P}H3}$$

If $M$ is the molecular mass of $\ce{H3PO2}$ then $E_\text{oxidation}=M/4$ (for change in oxidation state from $+1$ to $+5$) and $E_\text{reduction}=M/4$ (for change in oxidation state from $+1$ to $-3$)

Equivalent mass of $\ce{H3PO2}$ in this disproportionation reaction

$$= E_\text{oxidation}+E_\text{reduction}= M/4+M/4= M/2$$

Now, I am not able to comprehend that, why these two types of equivalent mass has been added to arrive the equivalent mass of $\ce{H3PO2}$.

My take: The concept of equivalent mass collapses in this situation!


texts: What is the reason for the acidic character in phenols?

texts:
I came across this concerning phenols:

  The hydroxyl group, in phenol is directly attached to
  the $\ce{sp^2}$
   hybridised carbon of benzene ring which acts as an
  electron withdrawing group. Due to the higher electronegativity of $\ce{sp^2}$
   hybridised carbon
  of phenol to which $\ce{–OH}$ is attached, electron density decreases
  on oxygen. This increases the polarity of $\ce{O–H}$ bond and results
  in an increase in ionisation of phenols than that of alcohols.

My concepts seem to be flawed, and hence I have few questions on the same.

When the $\ce{sp^2}$ carbon atom withdraws electrons from the oxygen atom, the oxygen's electron density decreases. How does this increase the polarity in the $\ce{O-H}$ bond? Shouldn't it be the opposite as oxygen becomes more electropositive due to the carbon atom? I'm missing something here.

Also, does the carbon atom in this case act as electron withdrawing because it is less electronegative than the oxygen atom?

Note that this question isn't about the comparison of acidic character between alcohols and phenols, and the relative stability of alkoxides and phenoxides.


texts: What is the ground-state electron configuration of V2+?

texts: Why do you get rid of the 4s^2 electron subshell first rather than 2 electrons from the 3d subshell?


texts: Can ascorbic acid be neutralized and keep it's elastic properties in dough?

texts:
Ascorbic acid (C6H8O6) is commonly used in dough to give it strength and elasticity. However, I need this dough to be alkaline, or at the very least neutral. I've used sodium carbonate (Na2CO3) before for this purpose but never at the same time with ascorbic acid.

If I use vitamin C in dough to make it elastic, as well as sodium carbonate to it neutralize it, will the dough retain the elastic properties caused by the ascorbic acid? What ratio of ascorbic acid to sodium carbonate creates a neutral solution? Thanks!


texts:
I was wondering if there is any other way to crystallize materials from a solution other than using supersaturation?

Thanks,


texts: The proper formula of sucrose: why both forms are correct and how one is transformed into another?

texts:
During preparations for my exam I've stumbled upon a tormenting question how it happens that the formula of sucrose is written in two different forms: the vertical and the horizontal ones:

The horizontal form

The vertical form

The vertical one seems quite obvious and logical when you know that the hydroxyl group on the second carbon in β-ᴅ-fructose directs up, but in the horizontal and more popular form the −OH directs as it was alpha form what's not true. How does it happen that both are correct?


texts: Calculating temperature change due to Joule-Thomson effect

texts:
I have a 10 L compressed argon cylinder with filling pressure of 10 MPa. According to Perry's Chemical Engineer's Handbook, argon's J-T coefficient (unit: K/MPa) is 3.7 at 0.1 MPa, 2.6 at 10 MPa. (Temperature is 300 K.)

When I open up the cylinder valve, 10 MPa argon in the cylinder will expand into 0.1 MPa atmosphere. So the $\Delta P$ is 9.9 MPa.

  How much will the temperature change?
  The initial temperature is 300 K.

$9.9 \times 3.7 = 36.63$

(Which means the temperature of argon outside the cylinder will be 263.37 K)

$9.9 \times 2.6 = 25.74$
Something in between (like when the J-T coefficient in effect changes continuously as the gas expands).


texts: I was thinking that it might be non aromatic since the ring is very big and it might bend just like COT (cyclo-octatetraene) does to avoid destabilization due to antiaromaticity but I don't know if the given does that or not.


texts: Comaparing melting points of group 14 elements

texts:
I found that melting point of $\ce{Sn(232°C)}$ is less than $\ce {Pb (327.5°C)} $ but i also saw that the bond enthalpy of $\ce {Sn-Sn(187.1 ±0.3 kJ mol^{-1})}$ is more than $\ce{Pb-Pb  86.6 ±0.8 kJ mol^{-1}}$ in the gaseous state.

I do not have any data for their bond enthalpies in solid state. And since melting involves breaking of bonds in solid state to convert it to liquid state should bond enthalpy of $\ce {Sn-Sn}$ should be less than $\ce{Pb-Pb}$ in solid state? Why or why not? I would like to know if here melting points depend on some other factor. Source -https://www.webelements.com/lead/compound_properties.html I want to know about Bond enthalpy comparison of $\ce {Sn-Sn} $ and $\ce {Pb-Pb} $


texts: Which bond is stronger, ionic or covalent? I have a lot of confusion about this.


texts: Half-life equation for 2nd order kinetics

texts:
My friends and I were doing some problems from this year's IChO Preparatory Problems (PDF from the 49th International Chemistry Olympiad (2017)) when we stumbled upon a question which we had some confusion with.

  Task 8. Decomposition of Nitrous Oxide
  Nitrous oxide decomposes exothermically into nitrogen and oxygen, at a temperature of approximately $\pu{565 ^\circ C}$.
  $$\ce{2N2O (g) -> 2N2 (g) + O2 (g)}$$
  This reaction follows the second-order kinetics when carried out entirely in the gas phase.

  8.1) If the reaction is initiated with $[\ce {N2O}]$ equal to $\pu{0.108 mol dm-3}$, what will its concentration be after $\pu{1250 s}$ have elapsed at $\pu{565 ^\circ C}$? The rate constant for the second order decomposition of $\ce{N2O}$ is $\pu{1.10\times10^-3 dm3 mol-1 s-1}$ at this temperature.

Task 8 details the kinetics of the decomposition of nitrous oxide. We were confused with part 8.1 of the task which required us to find the concentration of the reactant after a particular duration of time has elapsed, given the temperature, initial concentration and rate constant of the reaction. We approached the question using two different methods:

I approached it using the method, as suggested in the solutions manual, of using the integrated rate law for 2nd order kinetics and substituting the values provided into that equation. My answer was exactly that stated in the solutions manual.

However, they approached it by first finding the half-life using the equation for the half-life for 2nd order kinetics and then, finding the concentration after knowing how many half-lives have passed. Their answer was slightly off.

After substituting random values into the equations for both methods, I realised that the "half-life method" which my friends used only gives a reasonable approximation when the time elapsed < half-life, gives the exact value when the time elapsed = half-life and goes completely off when the time elapsed > half-life. Why is that so? Since the half-life equation for 2nd order kinetics is derived from the integrated rate law (as shown on Chemistry LibreTexts), shouldn't they give the same answer?


texts: Why would a reaction favor one isotope over another?

texts:
In my instrumentation class last semester, we were asked to read a short paper. The paper described a technique for determining whether dinosaurs were cold-blooded or warm-blooded based on the amount of a certain isotope in a sample of dinosaur bone.

What would cause a reaction to favor one isotope over another? In my general chemistry course, I learned that isotopes act similarly in chemical reactions. Of course, I have found over the years that pretty much everything taught in general chemistry was approximations probably so students don't feel inundated.


texts: What are the possible changes that might occur if I add an inert gas to a chamber containing another few different gases?

texts:
As an example, let's assume that we have a gas $\ce{P(g)}$ inside a chamber and when the temperature inside it increases to a certain value there is an equilibrium that prevails inside the system.

So for the sake of argument, let us assume that this equilibrium is:

$$\ce{P(g) <=> Q(g)  + R (g)},$$

And let's assume the figure below shows that chamber when equilibrium is established:

What I want to know is, what are the possible changes that might occur if I add an inert gas $\ce{I(g)}$ to this chamber?


texts: Why are N-H stretching vibrations often sharp and not broad?

texts: It is known that hydrogen bonding results in the broadening of peaks in the infrared spectrum of a molecule. Hydrogen bonding results in a spectrum of different bond lengths with different stretching frequencies. This results in a the functional group giving peaks of a whole continuous range of vibrational frequencies and hence, we see a broad peak. Broad peaks are most often observed from $\ce {2500}$ to $\ce {3000 cm^{-1}}$ for the stretching of carboxylic acid functionalities. Similarly, hydrogen bonding also results in alcohol $\ce {O-H}$ stretching giving broad peaks in the range of $\ce {3200}$ to $\ce {3600 cm^{-1}}$, albeit the degree of broadening is much less for alcohols. Amines are also able to form rather strong hydrogen bonds. However, amine $\ce {N-H}$ stretches often are not seen as broad peaks and are in fact, often sharp. Why is this so?


texts: Why is Ma*Va=Mb*Vb still valid for weak acids/bases?

texts:
I asked my chemistry teacher this today and didn't get an answer. It would seem to me that the equation for determining the morality of the unknown in a titration, MaVa = MbVb, would only work if the acid and the base were both strong.

I always interpreted the equation as a way to say (moles H+)=(moles OH-), but if the acid was weak, the moles of H+ would not simply equal MaVa, because the acid wouldn't fully dissociate, and the same for a base and OH-.

Yet the formula still works for both strong and weak acids and bases. Why?


texts: Is the behavior of a dilute strong acid the same as the behavior of a weak acid?

texts: My assumption is yes, as the $\mathrm{pH}$ levels of each will be similar and thus they have the same acidity. Is this correct or am I missing something?


texts: Arrhenius equation in Kinetics and Thermodynamics

texts:
It is always stressed that one should never mix Kinetics with Thermodynamic. How is it then possible to calculate the free energy of activation with the Arrhenius equation? As I understood, the Arrhenius equation and thus the activation energy of a reaction "belongs" to kinetics, whereas the free energy represents a term of Thermodynamics.

An example of the calculation I refer to can be found on page 7 of this link:
http://cbc.arizona.edu/classes/bioc460/summer/460web/lecture/EnzIntrod_11.pdf


texts: Reasons for dry conditions in substituition reactions with benzene

texts:
All substitution reactions of benzene must be carried out in dry conditions with a catalyst that produces a powerful electrophile.

This was a statement from my book. My question is, why must it be carried out in dry conditions?

What will occur if moisture is present?


texts: What is the nature of the bonding in cyclotriphosphazene?

texts:
The bonding in $\ce{(NPCl2)3}$ (and other compounds of the form  $\ce{(NPR2)3}$) has historically been described using the ‘Dewar island model’.

By analogy to benzene, $\ce{(NPCl2)3}$ is π-electron precise, containing 6-electrons in the π-system, and as such was thought to exhibit some degree of aromaticity.

The Dewar model accounted for this benzene-like structure by allowing phosphorous to use an occupied d-orbital to engage in a dπ(P)–pπ(N) interaction, forming the delocalised π-system of the phosphazene ring. This rationalised experimental observations that $\ce{(NPCl2)3}$ is (almost) planar and has equal P-N bond lengths which are somewhere between standard P-N (single) and P=N (double) bond lengths. What it fails to explain however is why other members of the series $\ce{(NPR2)n}$ do not show planarity.

Despite these flaws, and despite it being widely acknowledged that the d-orbitals aren’t capable of being involved in bonding to any great extent, the Dewar island model is still commonly found in inorganic chemistry textbooks and taught to undergraduates (possibly because its an easy to understand explanation and draws analogy to the familiar).

  Is there a better model to explain the bonding in $\ce{(NPR2)3}$ that is (1) consistent with the observed properties of the molecule, (2) makes sense in terms of the orbitals/interactions used (i.e. no invoking d-orbitals) and (3) can be backed up by calculation? [*]

[*]: My understanding is that negative hyperconjugation can be invoked, but this doesn't seem to be widely accepted and possibly isn't the most intuitive explanation for bonding by itself.


texts: Have IH₃ and IH₅ already been synthesized?

texts:
I've seen a paper by Sikalov [1] that says that $\ce{IH3}$ and $\ce{IH5}$ should be observable. Has anyone actually tried to synthesize such molecules?

References

Sikalov, A. A. Hypervalent Halogen Hydrides $\ce{HalH_n}$ ($\ce{Hal}$ = $\ce{Cl},$ $\ce{Br},$ $\ce{I};$ $n = 3, 5, 7)$: DFT and Ab Initio Stability Prediction. Theor Chem Acc 2019, 139 (1), 8. DOI: 10.1007/s00214-019-2524-0.


texts: Can chemical energy from food be stored in a battery?

texts: Suppose you built a machine that digested food in a similar way as humans do. Would it be possible, in principle, to extract the chemical energy from the digested food, turn it into electricity, and store it in a battery that powers the machine itself? Doesn't matter if it's practical or efficient, I just need to know if it's not something totally impossible. (I asked the same question on Electrical Engineering SE and someone suggested this SE would be more appropriate.)


texts: How much does butter shrink when frozen?

texts:
I just bought a butter dish which is a millimeter or two too small (the problems are that the corners are rounded which they forgot to mention before I ordered it and asked for the dimensions) to fit a piece of butter as it is sold in the supermarket. Since I don't want to return it my idea was to freeze the butter before I put it in this butter dish but for different reasons I can't make a "field test" just now (will update the question when I get the opportunity to do that). Instead I have to fall back to on theoretical answers.

How much does butter shrink when it's cooled from approximately 4°C (39°F) to -18°C (-0.4°F)?

Typically butter has about 1% salt, 82% fat and the rest is water.


texts: Why are reactions of acids with metals exothermic?

texts:
I realised the other day that I'm not sure why the reactions of strong acids with metals are exothermic. Any reaction is exothermic if there's more energy released from bonds being made than is used in breaking bonds, of course (using the word 'bonds' in a sufficiently loose sense).

In these reactions, metallic bonds are broken; covalent bonds are formed in hydrogen, but the hydrogen is in a gaseous state, so its molecules must be less attracted to each other than the hydrogen ions were to each other in the liquid. I'd vaguely guessed that the latter fact would make this an endothermic reaction (it works for sodium carbonate, after all) but evidently not!

Is there a rigorous way of calculating the total enthalpy change, or an easy explanation that I'm missing?

I guess I can calculate the enthalpy change of every one of the state changes involved, but it's not obvious that that's always going to come out negative (which I gather it does) so I feel like there's probably a less mathematical way of explaining this observation.


texts: I want to use lysol hydrogen peroxide multipurpose cleaner for cleaning my toilet. Is this a dangerous course of action?


texts: Why does the -OH group in β-naphthol direct the incoming diazonium salt towards the ortho position?

texts:
In the following reactions, the major product W is

I was doing this question which asks me the product of a diazotisation coupling reaction between diazonium chloride and β-naphthol. I know that the diazonium salt will act as an electrophile and compounds like phenol will direct it towards the para position, but I am not able to understand why the diazonium salt attaches itself to the ortho position of the -OH group in this compound.
The salt can also attach itself to the other benzene ring opposite to the -OH group. Also there are two ortho positions with respect to the -OH group. Can somebody please explain this to me?
This is the answer to the question:


texts: Alkylation of alkenes by nucleophilic substitution

texts: A double bond/alkene reacts as a nucleophile. I have never seen a reaction where it takes part in an $S_N1$ or $S_N2$ reaction with a halogenoalkane for example. This would presumably be a very useful reaction yet I have never seen it. I assume this is because it doesn't work. Is this the case? If so why?


texts: Bond stability of C-C in ethane, ethene, and ethyne

texts:
Which one of the three compounds has the highest $\ce{C-C}$ bond stability?

Ethane has $\mathrm{sp^3}$ hybridisation so less $\mathrm{s}$-character and lesser electronegativity compared to ethyne. Ethyne has high $\mathrm{s}$-character and high electronegativity. Therefore the covalent character of $\mathrm{sp^3-sp^3}$ in Ethyne should be stronger and have more stability right? the order would therefore be $\mathrm{sp-sp}$ >  $\mathrm{sp^2-sp^2}$ >  $\mathrm{sp^3-sp^3}$
Some online sites tell so, but others say since the $\ce{C}$ atoms are so close in ethyne that the nuclear repulsion would make it less stable. So ethane's $\ce{C-C}$ would be stronger and that therefore the order should be reversed
Edit: nutshell- sigma bond of which hybridisation is strongest among $\mathrm{sp}$, $\mathrm{sp^2}$ and $\mathrm{sp^3}$?
I took ethane, ethene, and ethyne just as a example


texts: I have a mixture that contains out of dirt/sand and salt. I want to extract and measure the salt. What would be the best way to extract the salt from this mixture?


texts: Why can we not compare the coupling constants to chemically equivalent (but not identical) protons to determine magnetic equivalence?

texts:
I have been learning about magnetic inequivalence today, and I find it quite hard to undersand. See, for example:

In this case, according to the book I am using, $\ce{H_\mathrm{a}}$ and $\ce{H_\mathrm{b}}$ may be chemical equivalents, but they are not magnetic equivalents, due to the fact that $J_\mathrm{{\ce{a-c}}}$ and $J_\mathrm{{\ce{b-c}}}$ are different. Which I understand, but should we not consider that there is a $J_\mathrm{{\ce{b-d}}}$ which is equal to $J_\mathrm{{\ce{a-c}}}$?
I do not understand why they are magnetically different, but both have to chemical equivalent protons, one in ortho and one in para position.


texts:
Grignards don't couple with alkyl halides. I know that thionyl chloride reacts with alcohols and other $\ce{-OH}$ group containing molecules to replace the $\ce{-OH}$ with a $\ce{-Cl}$. So we probably aren't making an alkyl halide from the alcohol with the thionyl chloride.

The book says that the starting product, which is an alcohol, attacks the sulfur in the $\ce{S=O}$ bond of $\ce{SOCl2}$. I got that the starting product should be an alcohol, but I did not expect the alcohol to attack the thionyl chloride.

Nevertheless, this generates an $\ce{R-O-SOCl}$ molecule, and the resonance-stabilized $\ce{O-SOCl-}$ ion is a good leaving group. This is the substrate that the Grignard can perform an SN2 type reaction on.

My question is: how common is it that alcohols attack thionyl chloride in this pattern? I'm guessing "not very common" because this would make thionyl chloride an undesirable reagent for making alkyl halides from alcohols. Is this reaction synthetically useful?


texts: Why do reference electrodes have porous frits or membranes as a salt bridge?

texts: From what I understand, they act as a salt bridge between the reference electrode electrolyte and the analyte solution (in a potentiometric titration). But why do we use partially permeable membranes or frits instead of making a normal salt bridge for the reference half cell?


texts: What is the difference between the titration of a strong acid with a strong base and that of the titration of a weak acid with a strong base?

texts:
Which of the following statements best characterizes the difference between the titration of a strong acid with a strong base and that of the titration of a weak acid with a strong base?

  A) Both the strong acid and the strong base are completely dissociated in solution whereas the weak acid dissociation equilibrium constant is small enough that there is a measurable amount of the un-dissociated acid present in aqueous solution.

  B) The equivalence point of a titration of a strong acid with a strong base may be observed with an indicator whereas the equivalence point of a titration of a weak acid with a strong base can only be observed with a pH meter.

  C) The titration of a strong acid with a strong base is a fast reaction whereas the titration of a weak acid with a strong base is generally a very slow reaction.

This website seems to indicate that choice C is correct.

For B, all I know is that the pH at the equivalence point does not equal 7.00 (pH > 7.00) for the weak acid titration.

For A, I know the first part of that sentence is true. Strong acids and bases are characterized by completely dissociating whereas weak acids do not dissociate to the same extent.  But is it true that there's a "measurable amount" of the un-dissociated acid present in aqueous solutions?


texts: Change in Enthalpy in Free Expansion of Ideal and Real gas against Vacuum

texts:
By free expansion, I am referring to gas allowed to expand freely against vacuum in a Joule Expansion.
If gas is ideal then change in Internal Energy '∆U' and change in Enthalpy '∆H' is zero.
(By ∆H = ∆U + nR∆T).
But I was wondering whether '∆H' would still be zero for real gas?
(I know that ∆U will be zero for real gas. I just want to ask about ∆H)


texts:
Is there a relationship between valence shell and formal charge of the atom......

Let's take an example.

  A carbocation for eg $methenium$ has a formal charge of +1,can we tell how many valence electrons it has using this.A carbon atom always forms 4 bonds but here it is only forming 3 bonds then surely there will be change in it's valence shell and the formal charge will be related to it?How about other atoms such as  ammonium ion.What will this positive charge signify....decrease in lone pairs or increase.Stuffs like that

I don't know much about formal charge so that's why I am asking such confusing questions.My teacher said to me that carbon always forms 4 bonds and since it is forming 3 bonds in cases like this , a positive charge will come to it.Same for nitrogen but he didn't tell me about the valence shell so that's why i am asking


texts: Physical meaning of thermal parameters dimension (Å²)

texts:
In single-crystal x-ray crystallography both isotropic and anisotropic displacement parameters $U_{ij}$ of thermal ellipsoids have dimension of square  angstrom ($Å^2$) as follows from the definition of Debye–Waller factor ($T$ is dimensionless):

For isotropic approximation (conditions of Bragg's law):
$$T_\text{iso} = 8\pi^2U\left(\frac{\sin \Theta}{\lambda}\right)^2 \to [U] = Å^2 \tag{1}$$
For anisotropic displacement parameters (ADPs):
$$T_\text{ani} = 2\pi^2 \sum_{i=1\\j=1}^3{H[i]H[j]U_{ij}e^\star[i]e^\star[j]} \to [U] = Å^2 \tag{2}$$
where $H$ is reflex's index; $e^\star$ is length of the reciprocal lattice basis vector.

In both cases $U_1$, $U_2$ and $U_3$ ($U_{ij}$ in general) are basically showing contribution of oscillation along three principal (orthogonal) axes and are measured in $Å^2$. So, is there any physical meaning that can be attributed to square angstrom in this case? At first glance, it seems rather confusing that a parameter that seems to represent a linear quantity is measured in square units of length.


texts: Solubility of potassium nitrate and potassium chloride

texts:
Why more water is needed to dissolve potassium chloride than potassium nitrate of equal amount? Is it to do with the reaction that occurs when the compounds dissolve or the properties of the compounds?

This is for an experiment on the effect of temperature on solubility in various chemicals.


texts:
This seems stupid question, but from many years I am studying that burning/combustion fossil fuel cause pollution because it releases $\ce{CO2}$.

I have recently read about $\ce{CFC}$ here, which is more dangerous than $\ce{CO2}$ and seems it is not release by burning of fossil fuel then why are scientist more concerned about fossil fuel instead of $\ce{CFC}$?

I want proper explanation Why fossil fuel is too dangerous?


texts: Why does the BET equation take into consideration a multimolecular-layer, even though it deals with chemisorption?

texts:
I came across the Brunauer-Emmet-Teller (BET) equation recently, and one thing that I found strange was an implicit reference to the formation of molecular multi-layer.

In the BET equation

$$
\begin{align}
\frac{P}{V(P^0 - P)} &= \frac{1}{CV_m} + \frac{C-1}{CV_m}\cdot \frac{P}{P^0}\, ; \tag{1}\\
C &= e^{(Q_1 - Q_2)/RT}\quad (C:\text{constant})\, ,\tag{2}
\end{align}
$$

where $V_m$ – monolayer adsorption amount, V – adsorption amount at the equilibrium pressure $P$, $Q_\mathrm{L}$ refers to the heat of adsorption of the second and higher layers of adsorbate onto the adsorbent.

Now according to my textbook, chemisorption only results in the formation of a molecular monolayer. Multilayers are formed by physisorption.

The thing is, I'm told the BET equation is an extension of Langmuir's adsorption isotherm for chemisorption at low pressures. If the BET equation applies only to chemisorption, then what is the point of including a term dependent on the formation of multilayers, when chemisorption doesn't even form a multilayer all by itself.

Is there something I'm overlooking here? The internet has not yielded any decent result in that regard.


texts: How do primary alcohols react with dihydropyrans

texts:
Can anyone also explain me the mechanism of this reaction?

I think it might be formation of acetal or hemiacteal reaction but I am not sure about it.


texts: Why do we need to add hydrogen to amorphous silicon?

texts:
I was recently studying about Staebler-Wronski effect observed in amorphous silicon (a-Si). I realised it was due to imperfections in the lattice structure and breaking of Si-Si bond to Si-H bonds.

So if hydrogen atoms will be less the effect will be minimum. Why do we add hydrogen atoms to a-Si?

Is is just to passivate the unsaturated Si atoms at the edges, or am I missing something?


texts: Is Pinacol rearrangement the source for the ring expansion?

texts:
I have no idea what's happening as in the product (the answer is (a)) there is a new ring being formed on the left benzene. But as I studied after $\ce{H2O}$ leaves, a carbocation is then formed on stabilized by the right ring.

Can someone please explain the rest of the steps of this reaction? The thing I don't get is how does the three-membered ring opening happens.
I attempted the question, but the answer that I came up with isn't the one matching in the book. Where did I go wrong with the mechanism?


texts: What's the relationship between supersaturation and temperature?

texts: In gravimetric analysis, what does supersaturation mean? And, how is it achieved by lowering the temperature, even though increasing the temperature makes a higher number of solute particles more soluble?


texts:
I have been trying to make muratic acid from salt and phosphoric acid (didn't know that it's made at 150 °C). After waiting a few days, a third of the time it was sealed by placing a container over it, I wanted to check if some HCl was created, by adding peroxide and etching a small PCB, after 2 days I noticed small white crystals and the solution turned green.

What are those crystals and why is the fluid green?


texts: Comparison of basic strength of benzylamine and ammonia

texts:
According to me, ammonia should be the stronger base for two reasons:

$\ce{-C_6H_5}$ group shows $-I$ effect, due to which electron density on $\ce{N}$ atom of benzylamine decreases
steric hindrance in benzylamine is more than that in ammonia

But their $\mathrm{pK_b}$ values are: benzylamine: $4.70$ and ammonia : $4.75$. High $\mathrm{pK_b}$ value of ammonia shows that it is actually less basic than benzylamine, contrary to my reasoning. Why is it so?


texts: The mechanism for phosphoglucose isomerase changing glucose  6 phosphate to fructose 6 phosphate shows histidine protonating the c5 oxygen and lysine deprotonation the c1 oxygen to form an open chain aldolase. Glutamic acid then deprotonates c2 to create an enediol intermediate and donates the proton to c1. For the proton to be transfered from c1 to c2 the c1 oxygen needs to be protonated and the c2 oxygen deprotonated. Does anyone know of a source that specifies the amino acid residue or residues that facilitate the deprotonation and protonation of the c2 and c1 oxygens?


texts: Relationship between structure and shock sensitivity for branched vs straight hydrocarbons and ammonium ions

texts:
In p. 137 of John D. Clark's Ignition! (in the new edition), Clark reports an interesting observation regarding the shock sensitivity of different isomers of alkyls and ammonium salts.

Specifically, he says that he compared the sensitivity of tetramethyl ammonium nitrate ("Tallulah") in $\ce{N2O4}$ with the isomeric chain ion $\ce{NH3+CH2CH2CH2CH3}$, with the latter being far more sensitive (58 cards vs 8 cards, on his card-gap test setup, which he explains in p. 69).

And, analogously, he compared neopentane with pentane (i.e. the same structures, swapping out $\ce{N+}$ for $\ce C$, again in $\ce{N2O4}$), and again got a fifty-card difference between the two, with pentane testing at 100 cards and neopentane much more stable at 50 cards:

  Again a difference of 50 cards, which meant that the ratio of the critical shock wave pressures due to structure was the same in both systems. I was fascinated by this coincidence, but never had the chance to carry the work any further. It's recommended to the attention of some future investigator.

Has this observation been followed up on? If so, what explains the coincidence?


texts: What concentration of small molecule binding is considered weak or strong?

texts: In the chemistry literature, I often see a stated concentration (nanomolar, micromolar, millimolar) followed by qualitative judgment on the potency of the small molecule for protein inhibition. What concentration range is considered weak, and what range might a small molecule be strong enough to be lead optimized?


texts: What happens to the water inside the egg when it is boiled?

texts: An egg contains 90% of water. When it is boiled, the water inside it cannot escape as water vapor because of the covering of calcium carbonate shell. After boiling, when the egg becomes solid the water cannot be seen. So what happens to the water inside the egg when it is boiled?


texts:
I'm supposed to produce dry and pure oxygen using the decomposition of hydrogen peroxide with a manganese dioxide catalyst.

$$\ce{2H2O2 (aq) → 2H2O (l) + O2 (g)}$$

The gas will be collected in a bottle by downward displacement of water. How can I safely move the oxygen gas through the drying agent without mixing in atmospheric gas?


texts: How can a methyl halide react by intramolecular SN2?

texts:
Out of the following, $\ce{CH3Br}$ doesn't react by which mechanism?

  SN2
  SN1
  E2
  Intramolecular SN2
  E1

My textbook gives 2, 3 and 5 as the correct answers, which means it does react by 1 and 4.

But how can a methyl halide react by intramolecular SN2, without a nucleophile present in the molecule? There's just a leaving group ($\ce{-Br}$).


texts: How to get the first step of the derivation of the Maxwell-Boltzmann distribution

texts: To derive the Maxwell-Boltzmann distribution the first step requires the knowledge that the equation will take the form $$f(v)=Ke^{-\epsilon/ kT}$$ where $\epsilon$ is the sum of the kinetic energies in the directions of the x,y and z axes. I understand that there needs to be exponential decay and why there will need to a constant. Also, I understand that the eponent needs to be dimensionless but why is KT used? This seems to pop up everywhere without much of an explaination of why (as in this case).  Can you help me understand how to get this first step? Thanks.


texts: Which reagents can directly oxidize ammonium ion into gaseous dinitrogen?

texts:
I have a simple question. I've looked on the internet and the only thing I found was the Anammox process - Anaerobic Ammonium Oxidation.  Wikipedia lists the reaction as:

$$\ce{NH4+} +\ce{NO2-}\rightarrow\ce{N2}+\ce{2H2O}$$

But only a few bactetria perform this process. I am looking for actual laboratory reagents that can oxidize ammonium ion to dinitrogen gas. My professor said that neither $\ce{KMnO4}$ nor $\ce{K2Cr2O7}$ can do the oxidation, and that one would have to use bleaching powder or $\ce{XeF2}$ instead. However I could NOT confirm his claim on the internet. Thus, I wish to know a list of such reagents which can do what I wish to. Thank you!


texts: Why doesn't the viscosity of water change much with temperature like it does for other substances?

texts:
I would like to know why water doesn't ever become like syrup before it freezes when many other liquids, such as hydrocarbons, seem to have a more gradual change from becoming more viscous and then turning solid.

As I understand it, the more viscous a material is, the stronger the inter-molecular forces are. When the liquid is heated up, the molecules have more kinetic energy and so they can more easily break free of these forces--the liquid will become less viscous.

Why doesn't water have the same spectrum of viscosity as other materials? It seems like it is either solid, or it has very low viscosity.


texts: Which is more reactive, chlorine radical or chloride ion?

texts:
Ions are very reactive for obvious reasons (i.e. Coulomb force); $\ce{Cl-}$ ions will be very quick to form an ionic bond with positive ions (unless inhibited, e.g. through being in a solution; let's consider both $\ce{Cl}$ and $\ce{Cl^-}$ to be in gaseous phase).

Chlorine atoms without reduction ($\ce{Cl}$), aren't charged, yet tend to combine into $\ce{Cl2}$, utilising a covalent bond.

Thus, both $\ce{Cl}$ and $\ce{Cl-}$ tend to form bonds. My confusion lies in the following:

Noble gases are chemically inert, $\ce{Cl-}$ has the electron configuration of $\ce{Ar}$, yet it's very chemically reactive.
Neutral atoms aren't as attracted to each other as ions, and could be considered more "chemically stable" than ions with higher charge. However, even though $\ce{Cl}$ has no charge, it still seems eager to react and get to the electron configuration of a noble gas.

In both cases, information seems conflicting, and perhaps a more clear explanation will make me understand the situation. Is one more prone to react than the other?

(N.B.: My knowledge on chemistry, maths, physics etc … stretches to (but doesn't include) quantum physics, so feel free to go all-out.)


texts: O-H infrared band dependence of alcohol concentration in water

texts: With regard to IR spectroscopy, how would the O-H band change as an alcohol solution was diluted with water? I am referring to any alcohol, but for the sake of example we can use ethanol. I think first that the $\ce{O-H}$ band shown would increase in intensity. I believe this is the case because the water is becoming a greater proportion of the mixture and water is explicitly made from $\ce{O-H}$ bonds whereas the $\ce{O-H}$ bond in ethanol only represents a fraction of the bonds in the molecule. Is this correct? Is there also a wave number shift that would occur too that I am missing?


texts: What does a fractional order of reaction mean for the mechanism?

texts:
I'm doing a high school/sixth form college investigation of the kinetics between magnesium ribbon and hydrochloric acid.

I have obtained a rate order was 1.5 w.r.t [H+] and hence the rate equation is rate = k[H+]1.5.

What would that mean about the mechanism?

I remember my teacher once telling me that a fractional rate order just means that there is an intermediate stage and each step has its own rate order which contributes to the rate equation - is this right?

Below is a pictorial representation of what my teacher told me:

Also, what would this mean for my rate-determining step? If the above is true, what would I choose as the RDS if they both contribute a different amount to the rate order?


texts: Did Berzelius unify the names of chemical elements using the Latin language?

texts:
I asked this question because the Chinese Wikipedia community is trying to decide whether it should use Latin names or IUPAC names for the first introductory sentence for its articles on chemical elements.

One of the central argument by those support Latin names is the statement that Swedish chemist Berzelius unified the names of chemical elements using the Latin language common to European countries.

They cite the source in Chinese language here:
http://www.cnki.com.cn/Article/CJFDTotal-ZHHJ198805015.htm

"Swedish chemist Berzelius first proposed to use Latin, a language common to European countries, to unify the naming of chemical elements, thereby changing the chaotic status of naming them." (My translation)

What I have found from the literature is that Berzelius's proposal helped unifying the symbols of chemical elements, but the names remain diverse in language sources (not all are Latin) and some remain disputed (not all unified). Thus, I gather that Berzelius's proposal helps, but it is far from the statement that he unified all the names of chemical elements using Latin. If so, it begs the question why IUPAC names for Gold, Silver, etc. are not Latin.

Thus, your help is needed to answer the question as stated in the title.


texts: Experimental heat of solution much higher than expected?

texts:
I conducted an experiment in which $2.0\ \mathrm g$ of $\ce{NaOH}$ was dissolved in $200\ \mathrm{mL}$ of distilled water. This took place in a well isolated calorimeter. A temperature probe was used to measure the temperature change of the solution, which had an initial temperature of $24.9\ \mathrm{^\circ C}$ and a final temperature of $39.6\ \mathrm{^\circ C}$. Then, the enthalpy change associated with the reaction is
$$\begin{align}
\Delta H &= -mc\Delta T \\
&= -(200\ \mathrm g)(4.184\ \mathrm{J/(g\ ^\circ C)})(39.7\ \mathrm{^\circ C} - 24.9\ \mathrm{^\circ C}) \\
&= -12.3\ \mathrm{kJ}
\end{align}$$
However, according to the accepted enthalpy of solution, the actual enthalpy change should be
$$\Delta H = (-44.2\ \mathrm{kJ/mol})(2.0\ \mathrm g/(40.0\ \mathrm{g/mol}))=-2.2\ \mathrm{kJ}$$

How is it possible that there should be more energy released experimentally than what is predicted theoretically? If anything, there should be less energy, as some will escape. The obvious factors can be ruled out, the temperature probe was only in contact with the solution, the calorimeter was very well insulated, exactly $2.0\ \mathrm g$ and $200\ \mathrm{mL}$ of sodium hydroxide and water was used. This experiment was also repeated, yielding similar results. I'm at my wit's end trying to figure this out.


texts: I believe that the G band (~1600 cm-1) shows the stretching mode of the graphene in a carbon nanotube (e.g. chiral, zigzag, armchair) and the 2D band (~2680 cm-1) shows the number of walls in the CNT. I vaguely remember there is some information that can be gleaned from the ratio of the two. Is this the case?


texts: Gaussian Calculations - What is the Basis?

texts: What am I actually changing when I click 631G(d) or 631G(d,p), etc. when I choose a "basis" in restricted Hartree Fock calculations? What is the difference between using an alternative basis?  Many thanks.


texts: I read that continuum in line spectra is noticed beyond a certain limit. What does it mean?


texts:
I have got this problem in my text book,

  Consider these three
  mercury manometers. One of them
  has 1 mL of water placed on top of the
  mercury, another has 1 mL of a 1 m
  urea solution placed on top of the
  mercury, and the third one has 1 mL of
  a 1 m NaCl solution placed on top of
  the mercury. Identify X, Y, and Z with
  these solutions.

I got the answer in answer sheet is X = ${H_2}O$ , Y = $NaCl$  and Z = ${(NH_2)}_2{CO}$ . Can any one please explain me? Thanks in advance.


texts:
What invariants related to geometrical structures that describe molecular geometry are used in chemistry?

Explanation: Here, Electronic model with highest prediction rate…, one can learn about electronic models. Now, I want to learn which invariants are used in all major models used (and why).

Definition of invariant: Invariants in chemistry used for model selection

Example of invariants in physics of ideal gas (invariance of the geometry of ideal gas with respect to Legendre transformations): http://arxiv.org/pdf/0811.0222v1.pdf


texts: I was doing a titration and using $\ce{NaOH}$ as the titrant. The analyte was a weak acid with a $\mathrm{p}K_\mathrm{a}$ of 4.90. Today I want to use another acid with a $\mathrm{p}K_\mathrm{a}$ of 4.50. Do I need to change the indicator from the last experiment? How close do the $K_\mathrm{a}$ or $\mathrm{p}K_\mathrm{a}$ values have to be in order for me to use the same indicator and still obtain accurate results.


texts:
The maximum no. of isomers (including stereoisomers) that are possible on mono-chlorination of the compound: 3,3-dimethylpentane is?
 The answer given is 5.

My working: The fourth carbon is chiral when chlorine is added to it, so it'd have an enantiomer, and there are two other carbons where chlorine can be substituted, so how is the answer 5?

$\ce{CH3-CH2-C(CH3)2-CH2-CH2Cl}$,
$\ce{CH3-CHCl-C(CH3)2-CH2-CH3}$ (this is chiral and would have an enantiomer),
$\ce{CH3-CH2-C(CH2Cl)(CH3)-CH2CH3}$

are the compounds I could make out.


texts: Is $\ce{H[AuCl4]}$ tetrachloroauric [III] acid or hydrogen tetrachloroaurate[III]? As per the rules I have studied the latter name is correct. Then why am I getting the former name mentioned everywhere on the internet as the IUPAC name, although Wikipedia does mention the other name (hydrogen tetrachloroaurate[III]) though not as the IUPAC name?


texts: How to generate fully coloured electrostatic potential maps in Avogadro?

texts:
I want to generate electrostatic potential maps of molecules using Avogadro, that show the colour scheme ranging from blue through green and yellow to red.

In this Youtube video, at 1:32, the video author does just that.

However, when I try the same thing on my Avogadro (version 1.2.0), it shows this:

How do i display the colourful electrostatic potential map on my computer? My computer has a 4 GB RAM and an NVIDIA GeForce 210 Graphics Card.

Thank you!


texts: How does a space group determine crystal structure?

texts: If I have an intermetallic and want to know the specific arrangement of atoms in the lattice, how can I determine that? What I mean is the Cartesian (xyz) position, or the (abc) positions in the lattice. In my case, I am working with Ni3Sn4, which has a space group C2/m. The space group diagram can be found here.


texts: When Tildens Reagent is added to an alkene does the product change to an oxime always?

texts:
I was reading about Tildens Reagent when I came across this..

Does this happen always?
Or is it when there is only a single hydrogen attached to the carbon?


texts: Which double bond is more electrophilic : carbon-carbon or carbon-oxygen?

texts:
Question

Attempt

It seems to me that the carbon-oxygen bond would be more electrophilic due to the higher electronegativity of oxygen. Hence I believe $\ce{CH3-}$ should attack the carbonyl site. But this doesn't seem to be the case.

Is it because that the intermediate carbanion can undergo resonance with oxygen, had $\ce{CH3-}$ attacked carbon- carbon double bond?

What can be a valid reason?


texts: About undocumented conventions(?) in PDB files

texts:
ATOM 22 N  GLN L 3 23.945 -2.849 106.974 1.00 15.00 N
ATOM 23 CA GLN L 3 23.125 -2.052 106.036 1.00 15.00 C
ATOM 24 C  GLN L 3 22.898 -0.648 106.616 1.00 15.00 C
ATOM 25 O  GLN L 3 22.613 -0.491 107.825 1.00 15.00 O

In every amino acid there are two O atoms; which one is described by the (in this example) fourth entry? (I guess it's the one that's next to the next amino acid's N, but then where are the coordinates of the other one or should this be obvious?)

ATOM 26 CB   GLN L 3 21.754 -2.682 105.749 1.00 15.00 C
ATOM 27 CG   GLN L 3 21.577 -3.299 104.379 1.00 15.00 C
ATOM 28 CD   GLN L 3 20.956 -4.676 104.431 1.00 15.00 C
ATOM 29 OE1  GLN L 3 20.940 -5.348 105.476 1.00 15.00 O
ATOM 30 NE2  GLN L 3 20.496 -5.137 103.279 1.00 15.00 N
ATOM 31 H    GLN L 3 24.339 -2.372 107.727 1.00 0.00  H
ATOM 32 HE21 GLN L 3 20.637 -4.559 102.496 1.00 0.00  H
ATOM 33 HE22 GLN L 3 20.049 -6.007 103.275 1.00 0.00  H

What's this entry's nr.31 supposed to describe? I thought that an entry without remoteness indicator (and branch designator) might be bound to the previous atom, but in this case the N's adjacent H atoms are already dealt with with entries 32 and 33.

Also, this doesn't quite follow the convention(?)* of increasing the branch designator by one each time a new branch emerges—is this usual when H atoms' positions are given as well?

* like here:

ATOM 1661 CG  TRP A 214 24.705  7.905 6.526 1.00 50.03 C
ATOM 1662 CD1 TRP A 214 23.435  7.531 6.857 1.00 49.65 C
ATOM 1663 CD2 TRP A 214 25.087  8.914 7.475 1.00 51.52 C
ATOM 1664 NE1 TRP A 214 22.999  8.246 7.947 1.00 51.68 N
ATOM 1665 CE2 TRP A 214 23.993  9.098 8.350 1.00 52.47 C
ATOM 1666 CE3 TRP A 214 26.251  9.675 7.670 1.00 52.68 C
ATOM 1667 CZ2 TRP A 214 24.019 10.027 9.407 1.00 54.73 C
ATOM 1668 CZ3 TRP A 214 26.279 10.600 8.724 1.00 53.86 C
ATOM 1669 CH2 TRP A 214 25.167 10.761 9.581 1.00 54.84 C


texts: Is it the solution energy or the reduction potentials (or both) that drives a galvanic cell?

texts:
I have received conflicting explanations for why the redox reaction in a galvanic cell occurs.
Explanation 1:

Some say that it occurs because the anodic metal dissolves more easily than the cathodic metal, and as such, the anodic metal will dissolve more quickly, becoming a positive cation that releases electrons (oxidizes). At the same time, in the cathodic half-cell, the positive cations in the solution will solidify on the surface of the cathode, due to rather wanting to be solid than an aqueous cation. However, these cations joining the cathode will add more positive charge than negative charge, and as such, the cathode will be positively charged. This will create a voltage between the electrons, and attract the electrons from the negatively charged anode, producing a current.
This means that the energy produced by a galvanic cell happens the system has less enthalpy when the anodic metal finds itself in a solution complex rather than a crystalline complex AND the cathodic metal finds itself in a crystalline complex rather than a solution complex.

Explanation 2:

Some say it occurs because of the reduction potential difference. The enthalpy change of an oxidation is always positive, and the enthalpy change of a reduction is always negative. If the cathodic ion's reduction has negative enough enthalpy change to make up for the positive enthalpy change of the anode's oxidation, then the reaction will happen. If the anode oxidized and the cathodic ion reduces, the resulting system will in total be of less enthalpy. Therefore, the redox reaction happens.

So, both explanations involve the fact that the energy of the system is lower if they react in the respective ways, but it has different explanations for exactly which process it is that involves the ultimately negative enthalpy change. Is it the solvation of the anode + the solidification of the cathode  ion that produces the negative enthalpy change (and therefore the energy to be used), or is it the oxidation of the anode + the reduction of the cathode ion that produces the negative enthalpy change? Or is it a combination of both?
Looking at types of corrosion, there can happen a redox-reaction without an electrolyte (dry corrosion), which means solvation isn't necessary for redox in general, but perhaps is needed for a redox reaction to happen when the reactants aren't in physical contact.


texts: Effects Guiding Electrophilic Aromatic Substitution

texts: This is a question which I come across in an examination. I know the answer and also know the solution. Well when I first saw this problem I didn't know how to approach this problem and I think I will still not be able to predict the correct answer of a question which will be based on this question's type . I am not asking that this is "this" reaction and it must proceed like" this " ,but what I want is how will you approach this problem . What will you think on first look of the problem. What all things you will observe from question and also do write what you think the answer must be . Also BEWARE THIS HAS MULTIPLE ANSWERS CORRECT. I am not telling you the answer because it would be easier to explain that answer . Also, please those who have seen this problem earlier. Please resist yourself from posting answers.


texts: A recent article (ACS Omega 2021, 6, 8021−8027) confirms the stability of nanobubbles with theoretical principles. Nanobubbles, having a size in the range of 50-500 nm, are reported to be metastable, i.e., stable in various liquids for times ranging up to weeks. Is the inside of the bubble filled with a gaseous form of the liquid surrounding the bubble, or with some other gas? Are there repeatable observations of nanobubbles? Is the theoretical derivation even correct?


texts: Solvent Effects in Friedel–Crafts Reaction

texts:
While reading about the factors affecting the product of Friedel–Crafts acylation with acetyl chloride, I came across a reaction involving napthalene in two different solvents: in nitrobenzene substitution took place at the beta position; in carbon disulphide substitution took place at the alpha position.

What is the reason for this?


texts: Why do sp2 carbons tend to prefer eclipsed conformations whereas sp3 carbons prefer staggered

texts:
I am a second year undergraduate and have come across this when studying stereochemistry and conformations and have been unable to find a satisfactory answer.

I know that $\ce{sp^3}$ carbons prefer anti-periplanar and gauche conformations due to the overlap of filled orbitals with empty orbitals but cannot seem to find an answer for why $\ce{sp^2}$ carbons prefer an eclipsed conformation. I was possibly thinking about the need to avoid $\pi$ electrons however I am not sure.


texts: Generating electron density from protein coordinate (PDB)

texts:
Normally protein coordinates are generated from electron density, such as that from X-ray scattering experiment. In my case, I want the reverse - PDB to electron density mesh. I thought it was more trivial and a program should be available. But Google did not give me any luck.

Is there any existing python library/program which converts protein coordinate (pdb) into electron density mesh (custom resolution)? If not, how should one proceed? The orbital and atomistic electron density varies among atom types.

Your suggestion appreciated.

Edited:

The precision of electron density I am interested in is ~ 1-2A so hopefully DFT level might not be necessary in my case. The aim is to visually resolve sidechain atoms. Since there could be manipulation of the PDB upstream, some crystal structure information could be lost.

Indeed the raw electron density might provide such information but a unified treatment of PDB coordinate homogenizes structures, making a more fair comparison between them, specifically in my case.


texts: Oxidizing 2-Methylpropan-2-ol using potassium dichromate. Why is heating required?

texts:
In Chemistry class, we had to combine $\ce{K2Cr2O7}$ with 2-Methylpropan-2-ol and heat it for the oxidation to occur.

But why do we have to heat the mixture when, for example, butanol, can be oxidized via use of the same reagent but without heating it?


texts:
I have learnt for many years that rate of reaction is the rate of change of concentration of a reactant or product with respect to time. I never questioned this before, but recently I have been learning about the rate equation and the order of the reaction with respect to a reactant. Seeing the graphs of how concentration changes with respect to time when you have a different order with respect to a reactant (as shown here)

It seems to me that choosing a different reactant to measure the rate of change of concentration of would give you a different rate of reaction? So how is the rate of a reaction defined?


texts: Does relative amount of lithium and cobalt oxide change in recharged battery?

texts:
There is a question on my assignment about stoichiometry. I spent 2 whole days searching and review this topic but still clueless.

Reaction in lithium ion battery
$$
\ce{Li(s) + CoO2(s) → LiCoO2(s)} \, .
$$
When the battery is recharged, electrical energy will reverse the reaction. How do the relatives amounts of lithium and cobalt oxide change as the battery is recharged and how?


texts: Claisen Condensation vs. Trans-Esterification

texts: In the Claisen condensation, an alkoxide $\ce{RO-}$ acts as a base. However, in trans-esterification, an alkoxide $\ce{R'O-}$ attacks the carbonyl carbon of an ester as a nucleophile. Is this because a different 'R' group is used in trans-esterification?


texts: Why can you not make a compound with a quaternary alpha carbon using malonic ester?

texts:
So my textbook tells me that using a malonic ester to make a quaternary alpha carbon is impossible (I get that this might be hyperbole). However, it doesn't explain why and I don't understand why.

My thought was that after the first addition the tertiary compound would be too bulky to act as a nucleophile. However in the next section, an ethyl acetate is treated with LDA and acts as a nucleophlile 3 times to create a quaternary alpha carbon.

I also considered that you'd be making a tertiary carbon anion to make a second addition to a malonic ester's alpha carbon. However you also make a tertiary carbon anion using LDA on ethyl acetate and then alkyl halides.

I've added a screenshot of my textbook. Skip to the part in parenthesis if you want to read it.


texts: Are there any chemicals with this structural skeleton?

texts:
Is there a chemical that has the bond structure like below?

There are 5 atoms linking together.
Two of them have 4 bonds. (They are different atoms.)
Another two of them have 3 bonds. (They can be either same or different atoms.)
The last atom has only 2 bonds.

Suggested SMILES for unknown $\ce{X}$ elements is [X]2[X]14[X]3[X]1[X]234

Are there such kinds of chemicals?


texts: Is there a simple and inexpensive way to generate nitrogen gas?

texts: It's fairly easy to generate a significant yield of hydrogen gas simply by reacting zinc metal with $\ce{HCl}$ or aluminum with $\ce{NaOH}$ solution. But is there a simple and inexpensive chemical reaction that generates a significant yield of pure nitrogen gas?


texts:
Why is there two different kinds of hydrogen bonding in solid bicarbonates $\ce{NaHCO3}$ and $\ce{KHCO3}$? In both cases we consider anions of each for hydrogen bonding .

The anions involved in hydrogen bonding are the same for $\ce{NaHCO3}$ and $\ce{KHCO3}$. But, why is there a difference in hydrogen bonding?


texts: Chemical Kinetics / Rate Question -- Error in Textbook Question/Answer?

texts:
I am reading Kaplan's General Chemistry MCAT Review 2018-2019, and think that one of its chemical kinetic questions is wrong. (Or perhaps I am simply missing something). I have attached an image of the question, which is easier than typing out as it includes the standard table of concentrations at different trials.

The answer reads: "In the first two trials, the concentration of $\ce{XH4}$ is held constant while the concentration of $\ce{O2}$ is multiplied by 4, and the rate of the reaction also increases by a factor of approximately 4..." It ultimately comes up with a rate of $k\ce{[XH4]^2[O2]}$

Am I completely missing something? My first question is, is the book's answer right? If it is not, is the problem solvable (i.e. does the table make any sense at all)? I've tried to come up with rates using the table and encountered the following issues. Please let me know if I am right in approaching the question in this way:

If you try to find the rate with respect to $\ce{XH4}$ using trials 1 and 3, I believe you get an order of 3. However, if you try to find the same rate using trials 1 and 4, you get 4. This isn't normal, right? Maybe an example of a mixed order reaction? Or just a mess up?
How do we interpret the data from trials 3 and 4? The concentration of neither reactant changes and yet the rate doubled. If we ever see something like this in a table, does it suggest that the reaction is 0 order? Or can we not make that leap? And is it even possible to have this data alongside the other data in the table?
It seems to me that, based on Trials 1 and 2, the rate is 0 order with respect to $\ce{[O2]}$. Is that a correct interpretation?

Thank you so much!


texts: How does one actually get the energy from the Kohn–Sham equations?

texts:
This might be a silly question, but how does one acquire the energy of the system from the Kohn–Sham equations?

$\left[ -\frac{1}{2}\nabla^2 + V_{eN}(\vec{r}) + V_{ee}(\vec{r}) + V_{xc}(\vec{r}) \right]\phi_i(\vec{r})=\epsilon_i\phi_i(\vec{r})$

Where $\nabla$ is the Laplacian operator, $V_{eN}(\vec{r})$ is the electron-nuclei attraction, $V_{ee}(\vec{r})$ is the electron-electron repulsion, $V_{xc}(\vec{r})$ is the exchange-correlation potential, $\phi_i(\vec{r})$ are the one-electron wave functions and $\epsilon_i$ are the orbital energies.

Assuming that we run through this set of equations for each electron, we get a set of orbital energies: $\epsilon_i \cdots \epsilon_N$. How is the overall total energy of the system then calculated?


texts: Obtaining magnesium oxide from magnesium hydroxide

texts: What's the simplest and safest DIY way to obtain magnesium hydroxide to magnesium oxide?


texts: I am working with zinc dust (particles of 10um). I want to make a stable dispersion of this dust with arabic gum. The problem is that the particles are still too big, the solution rapidly settles.... My idea to decrease particles size was to use HCl to corrode Zn into Zn2+. And then stopping the reaction by adding soda. I thought getting something light but instead I have a precipitate less soluble than my first zn solution. What happens ? What would be the best strategy to decrease zn particles size ?


texts: The product of a reaction series involving 1,3-dithiane, 1-chloro-3-iodopropane and butyllithium

texts:
I encountered this question while solving an objective paper.

$\ce{BuLi}$ is a strong base and it can be used to abstract a proton from the substrate. Low temperature favours substitution more than elimination. So my idea was that the ring will break up $\ce{Li}$ will be substituted in place of two $\ce{S}$ atoms. The next product should involve formation of a six membered saturated ring but I am unable to proceed further. What is going to happen?


texts: Which has the highest melting point among NaF, NaCl, NaBr, NaI?

texts: I've been trying to understand why $\ce{NaF}$ has the highest melting point among all of the given solids. I thought it would be $\ce{NaI}$ as it will have the biggest molar mass among them which would mean it has the strongest intermolecular forces. Is it electronegativity difference or molar mass that you look at when analysing intermolecular forces? Am I missing something or misunderstanding something? Thank you very much.


texts:
I am considering the following chain reaction:
$$\begin{align}
\ce{A_0 + B <=>[$N\cdot k_+$][$k_-$]A_1\\
A_1 + B <=>[$(N-1)\cdot k_+$][$2\cdot k_-$]A_2\\
A_2 + B <=>[$(N-2)\cdot k_+$][$3\cdot k_-$]A_3\\
...\\
A_{N-2} + B<=>[$2\cdot k_+$][$(N-1)\cdot k_-$]A_{N-1}\\
A_{N-1} + B<=>[$k_+$][$N\cdot k_-$]A_N} \\
\end{align}$$
Initial condition are $A_0 = 1, A_1=0, ... ,A_N=0$ and $B$ can vary from 0 to 1, $k_+$ is faster than $k_-$.

I have noticed (trough extensive numerical simulations) that result of this chain: $A_N$ is identical with the product of the following reaction in the power of N.
$$\begin{align}
\ce{A_0 +B&<=>[$k_+$][$k_-$]C} \\
\end{align}$$

Meaning that
$$\begin{align}
\ce{ $ [A_N]=[C]^N$} \\
\end{align}$$

I am wondering how to check this result analytically. I would like to know what to start with.

Thanks!

PS. I have looked at the ODEs and so far my calculations failed to prove the point, but I am not sure about my directions.


texts: Gold's atomic structure and bonding in relation to the separation techniques used

texts:
How is Gold's atomic structure and bonding related to the separation techniques used to distinguish it from other substances?

I'm just confused on what I'm actually searching for, I have read so many blogs on Gold extraction, refinement, occurences and more topics, and either I'm skipping the important parts or the answer's just not there. What can I search to find what I'm looking for? The separation technique I chose is flotation, can someone lead me in the correct path and/or give me a few hints on what to start of with? Thanks in advance, much appreciated!


texts: What is the mechanism for this intramolecular SN1 reaction?

texts:
What is the mechanism for the following intramolecular $\mathrm{S_N1}$ reaction?

For this question, my professor hinted at an intramolecular reaction, and he asked us to recall the bromonium ion as well. As such, I believe the $\ce{SMe}$ group attacks the open carbocation when $\ce{OTs}$ leaves. I think I understand how the left-side enantiomer is formed: $\ce{SMe}$ attacks the open carbocation, then water attacks from the back because the front-side is occupied by the hydrogen (not shown). However, what is the mechanism for the right-side enantiomer? How does the $\ce{SMe}$ end up in front (on a wedge) along with water after hydrolysis?


texts: Proton transfer equilibrium in bisulphite adducts

texts:
In the addition of $\ce{NaHSO3}$ to aldehydes and methyl ketones (higher ketones do not respond well to this reaction), crystalline addition products are formed. An $\ce{-SO3H}$ and an $\ce{-OH}$ group are attached to the same carbon.

$$\ce{R2C=O + NaHSO3 -> R2C(OH)(SO3^{-}Na^+) <=> R2C(O^{-}Na^+)(SO3H)}$$

The line I read online, bothering me is:-

  "The proton transfer equilibrium lies to the right for most ketones
  and to the left for most aldehydes."

What is the reason for this (assuming that it is correct in the first place)? Since the sulphonic acid group is more acidic than the hydroxyl group, should not the proton tranfer equilibrium lie towards the left for both the cases?


texts: How to effectively induce the bending motion of carbon dioxide?

texts:
I would like to know how to effectively induce the bending motion of $\ce{CO_2}$ with femtosecond IR lasers. In other words, how to effectively populate bending vibrational states in $\ce{CO_2}$ neutral or $\ce{CO_2}$ cation?

The ground state of $\ce{CO_2}$ is linear, but the first electronic excited state is bent. Does it mean the bending motion can be more efficiently populated on the electronic excited state? What is the energy gap between the ground state and the first excited state of $\ce{CO_2}$? Is it possible to achieve efficient excitation with a strong IR laser pulse?


texts:
In my class test, I was asked this question:

Which mechanism would be followed by a certain reaction with good
leaving group?

E1 reaction

E2 reaction

No reaction

both E1 and E2

I answered 4 because they both occur simultaneously the main difference comes in the amount of product formed by them. But, I was awarded with negative marks.
Can anyone please tell if I was wrong on my part or my teacher?


texts: Best chair configuration for trimethylcyclohexane matching a specific Haworth projection?

texts:
Which option best depicts trimethylcyclohexane shown in the Haworth projection below?

I thought B because

All the methyl groups are equatorial and equatorial groups are more stable.
All the methyl groups look as spread out as much as possible, reducing steric repulsion.

But the provided solution states that-

Although A,B and D could all be said to represent the chair form, the best depiction will show the methyl groups repelling one another as far as possible. The arrangement in A with two equatorial and one axial methyl groups makes A the best depiction.

Also, when converting Haworth to Chair, do we have to match the upward facing groups on the Haworth to upward facing positions on the chair?
i.e. the Haworth has 2 upward methyl groups and 1 downward facing methyl. But in A, the left equatorial one is facing upward (as axial in that position is downward), the middle axial methyl is upward, and the right equatorial methyl  is downward (as axial in that position is upward). This doesn't match the Haworth.


texts: Calculating laser wavelength/power to cause emission of light in a gas?

texts:
It's been a long, long time since I've had to worry about electron excitation levels and band gaps. Please forgive (and correct!) my terminology and misconceptions.

I've become interested in volumetric displays. In particular I'm looking at a pair of lasers scanning a volume of gas such that the intersection of the lasers would supply enough energy to cause the gas to emit visible light. Since this is the start of my research I would like to investigate a number of gasses in order to determine a number of gasses which might be suitable for this application. I have, however, forgotten how to determine the amount of energy needed to cause an outer shell electron to emit a photon, and then trying to back-calculate the required wavelength(s) and power requirements of the laser emitters.

I'm looking for some information on how to identify the required information for a given gas and how to calculate the energy required to cause visible light emission, and also information on how the wavelength of laser light impacts the ability of the gas to absorb the energy with the intended effect of emitting visible light. Links to introductory texts are always helpful, as are answers which help me get the terminology correct so that I can improve my searches for this information.


texts: Finding electron configuration by following the Aufbau principle

texts:
In the question, "Electron Configuration of Tellurium", there is mention of the 'follow yellow brick road' method of finding electron configuration.

What I'd learned in the past was to find the nearest noble gas (in the row above the element of interest) and count from there.

I searched in Google for this method and see that it appears to also called the Aufbau principle & diagonal method. However I'm not getting a good grasp on how it works.

Could someone explain this method to me?

Also, would this method work for something with a weird electron configuration, like copper?


texts: What does this curve over the C-B bond mean?

texts: I have come across this notation in a question I am trying to answer and am unsure of what exactly it means, can anyone clarify what this represents?


texts: Calculating numbers of moles at equilibrium given the volume of mixture and initial concentration of reactants

texts:
The equilibrium between three substances, A, B and C Is shown below.
$$\ce{A(g) + B(g) <=> C(g)}$$
Initially there were $\pu{0.1 mol}$ of A and $\pu{0.2 mol}$ of B in the reaction mixture. A and B reacted together to produce an equilibrium mixture containing $\pu{0.04 mol}$ of C. The total volume of the mixture was $\pu{2.00 dm3}$. Calculate the number of moles of A and B at equilibrium.

I honestly don't know how the answers are $\pu{0.08 mol}$ and $\pu{0.18 mol}$. I got the answers to be $\pu{0.06 mol}$ and $\pu{0.16 mol}$ by subtracting $\pu{0.04 mol}$ from each of $\pu{0.1 mol}$ and $\pu{0.2 mol}$.
Can someone please help?


texts:
I'm still rather confused as to how the common tangent construction ensure the chemical potentials are equal in the two phases?
(Also, if the one-phase regions and the two-phase metastable regions both concave upwards, why do the one-phase regions not undergo phase separation upon nucleation?)


texts:
I was reading about Group 15 and came upon the following:

  The penultimate shell in N contains 2 electrons (saturated), in P contains 8 (saturated), in Arsenic 18 (saturated) while antimony and bismuth contain 18 electrons (unsaturated) each.

What does the author mean by saturated and unsaturated?


texts: Two different methods to express the equilibrium constant give different results

texts:
$\pu{2.0M}$ of $\ce{I2}$ and $\pu{2.0M}$ of $\ce{Br2}$ are initially present in a reaction mixture. Calculate the equilibrium concentration of $[\ce{I2}]$ , $[\ce{Br2}]$ and $[\ce{IBr}]$ at $\pu{425K}$. $K_c=100$
Equation: $\ce{I2 + Br2 -> 2IBr }$

1st method

Equation:$\ce{I2 \ \ \ + \ \ \ Br2 ->\ \ \ \ 2IBr}$
Initial: $\ \ \pu{2.0M}\ \ \ \ \ \ \pu{2.0M} \ \ \ \ \ \ \ \ \ \ 0$
Change:   $\ \ x \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x \ \ \ \ \ \ \ \ \ \ \ \ \ 2x$
Equilib:     $\ \ 2-x \ \ \ \ \ \ \ 2-x \ \ \ \ \ \ \ \ \ \ 2x$
$K_\mathrm c =\frac{(2x)^2}{(2-x)^2}=100$

2nd method what if I separate $2\ce{IBr}$

Equation: $\ce{I2 \ \ \ + \ \ \ Br2 ->\ \ \ IBr \ \ + \ \ \ IBr }$
Initial:     $\pu{2.0M}\ \ \ \ \ \ \ \pu{2.0M}\ \ \ \ \ \ \ \ \ \ \ \ 0 \ \ \ \ \ \ \ \ \ \ \ \ 0$
Change:    $\ \ \ x \ \ \ \ \ \ \ \ \ \ \ \ \ x \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x \ \ \ \ \ \ \ \ \ \ \ \ \ x$
Equilib:       $2-x \ \ \ \ \ \ 2-x \ \ \ \ \ \ \ \ \ \ \ \ \ \ x \ \ \ \ \ \ \ \ \ \ \ \ x $
$K_\mathrm c =\frac{(x)(x)}{(2-x)^2}=100$
So which one is actually right and which one is wrong? Why?
The idea to use the second method came to my mind because of the the definition:

The equilibrium constant is a ratio of the concentration of the products to the concentration of the reactants

If $\ce{aA +bB \ —> cC + dD}$ (1)
$K_\mathrm c = \frac{[\ce{C}]^c.[\ce{D}]^d}{[\ce{A}]^a.[\ce{B}]^b}$
If I separate : $a\ce{A} = \ce{A}+\ce{A}+...+\ce{A}$ ($\ce{A} a$ times )
Same thing with $b\ce{B}, c\ce{C}$ and $d\ce{D}$, the equation (1) becomes:
$(\ce{A}+\cdots+\ce{A})+(\ce{B}+\cdots+\ce{B}) \ce{—>}(\ce{C}+\cdots+\ce{C})+(\ce{D}+\cdots+\ce{D})$
$K_\mathrm c = \frac{([\ce{C}]\cdots[\ce{C}])([\ce{D}]\cdots[\ce{D}])}{([\ce{A}]\cdots[\ce{A}])([\ce{B}]\cdots[\ce{B}])}$=$ \frac{[\ce{C}]^c.[\ce{D}]^d}{[\ce{A}]^a.[\ce{B}]^b}$ (Proved)
So, by using the second method, how and why is it not right ?


texts: Why does soap reduce surface tension of water

texts: One explanation I read is that soap's long non-polar end will seek the air at the interface between water and air, and that the ionic end will form ionic-dipole bonds with the water. In the process of moving to the surface, the soap molecules force apart the water molecules, and hence the water molecules no longer have hydrogen bonds with each other, and the surface tension is weakened. However, wouldn't the ionic heads of the soap molecules just form stronger ionic-dipole bonds with the water, increasing inter molecular forces, and therefore increasing surface tension? What is the true explanation for why soap reduces surface tension of water?


texts:
I just started with Molecular dynamics simulations. My background is computer science but I'm learning about scientific computing and thus my jump into MD.

Having said that, I was asked to calculate the percentage of each conformer in vacuum at a certain temperature of the Methylcyclohexane molecule. Assuming that entropies and molar volumes are identical.

Can someone point me out to some website or something where I can see how to calculate this?


texts: Constructing phase diagram given temperature-concentration-phase data

texts:
This question may look straightforward to be answered but somehow I can not figure it.

I received these papers [1-2]. Here, the papers (both papers study same system) provide complete information of phases in every point. What I am still mulling on is that usually I was given the phase diagram and locate compositions and phases in the phase regions. Suppose that the phase diagrams are not shown, how can I draw the phase regions from these points? How can I know that at some points outside the data makes transition to other phases when the temperature or composition is varied?

I would be very happy if someone can explain me to draw the phase regions as shown in the papers.

Thank you.

References

Campbell, A. N., Campbell, A. J. R. J. Am. Chem. Soc. 59, 2481-2488 (1937).
Rhodes, F. H., Markley, A. L. J. Phys. Chem. 25, 527-534 (1921).

Images

From ref. 1

https://pasteboard.co/J54SVM6.png

https://pasteboard.co/J54T2yI.png

From ref. 2

https://pasteboard.co/J54S1VH.png

https://pasteboard.co/J54SqoS.png

https://pasteboard.co/J54SDhZ.png

https://pasteboard.co/J54SM7y.png

Text about above figure


texts: Calculating molecular weight of an acid based on given values of mass, volume, pH and pKa

texts:
This is what I thought was an easy problem but according to a given answer I am doing it wrong:

  $\pu{11 mg}$ of a monoprotic acid was dissolved in $\pu{0.5 l}$ of water. The resulting $\mathrm{pH}$ of said solution was measured to be $5$. What is the molecular weight of said monoprotic acid? $\mathrm{p}K_\mathrm{a} = 6.$ $(t = \pu{25°C})$

My solution

Given values are:

$$m = \pu{0.011 g} \qquad V = \pu{0.5 l} \qquad \mathrm{pH} = 5 \qquad \mathrm{p}K_\mathrm{a} = 6$$

Formula used to calculate molecular weight:

$$M = \frac{m}{n}$$

Formula used to calculate concentration of acid in the solution, that is, the (hopefully correct) formula for calculating the acid equilibrium constant:

$$K_\mathrm{a} = \frac{[\ce{H+}][\ce{A-}]}{[\ce{HA}]}$$

Formula used to calculate molar concentration:

$$C = \frac{n}{V}$$

Putting them together:

$$M = \frac{m}{\frac{[\ce{H+}][\ce{A-}]}{K_\mathrm{a}}\cdot V} \label{eqn:alpha}\tag{α}$$

Concentration of $\ce{H+}$ and $\ce{A-}$ based on $\mathrm{pH}$ value:

$$[\ce{H+}] = [\ce{A-}] = 10^{-5}$$

Calculating the acid equilibrium constant from $\mathrm{p}K_\mathrm{a}$:

$$K_\mathrm{a} = 10^{-6}$$

Result:

Entering the above vaules for $m,$ $V,$ $K_\mathrm{a},$ $[\ce{H+}]$ and $[\ce{A-}]$ into equation \eqref{eqn:alpha} yields the molecular weight of $\pu{220 g mol-1}$. This is answer is wrong, supposedly. Did I make any mistakes?