texts: Formation of intimate ion pair by halogenoalkanes

texts:
I was recently doing this organic chemistry question that tested on the concept of the formation of the intimate ion pair in the nucleophilic substitution reaction at an $\ce {sp^3}$ carbon:

$\ce {RX -> R^+||X^- -> R^+ + X-}$

This mechanism is responsible for the slight retention of configuration during an $\ce {S_N1}$ reaction. It was mentioned that the formation of the ion-pair is more likely to occur for a chloroalkane than for a bromoalkane. In fact, it was written that there would be complete racemisation in the case of the bromoalkane while the chloroalkane would have slight preference for retention over inversion.

This seems to make sense since the $\ce {C-Cl}$ bond is stronger than the $\ce {C-Br}$ bond and secondly, the $\ce {Cl^-}$ ion is more charge-dense and is more likely to stay close to the carbocation after it is formed due to favourable electrostatic attraction. However, I have not read about this before from any authorative textbook on organic chemistry so I would just like to verify the validity of this assertion.

Also, can we extend this and assert that the formation of the intimate ion-pair is more likely to occur for bromoalkanes then for iodoalkanes based on a similar line of reasoning?


texts: Why is 1,2,3,4,5,8-hexahydronaphthalene more stable than 1,4,4a,5,8,8a-hexahydronaphthalene?

texts:
Why is 1,2,3,4,5,8-hexahydronaphthalene (1) more stable than 1,4,4a,5,8,8a-hexahydronaphthalene (2)?

A follow-up question is about stability being estimated by counting the α-hydrogens.
In the first case, do we consider α-hydrogens individually for each double bond, or are common hydrogens only taken once?  If it is the former, then the answer would be 12, or else 8. Which one is correct?
If it is the latter, both have an equal number of hyperconjugating structures, i.e. H = 8. Therefore the stability of both must be equal. Is this wrong?


texts: What are the physical properties of exotic ice?

texts:
This chart shows the phases of water that form at various combinations of pressures and temperatures.

It has multiple exotic forms of ice (labeled II through XV) listed. What are the physical property differences between these exotic forms of ice, regular ice, and each other?


texts: Reaction speed of Na2CO3 with vinegar vs that produced by NaHCO3 with CH3COOH

texts:
I'm working on a project requiring the easy production of a gas not corrosive to "normal" household materials (e.g. carbon dioxide). I settled on vinegar (acetic acid) and baking soda or washing soda, as it is very easily available to most people. Looking at the chemical formula for both sodium carbonate and sodium bicarbonate, I can assume that roughly the same amount of gas will be produced by the reaction of both with vinegar.

However, is there any difference at all in reaction speed? I don't care about the end product as long as it can be washed down the drain.


texts: There is a line cutting benzene ring what is that called.


texts: What wavelength of light is released when an electron drops an energy level in complexes?

texts: I know that the color of transition metals is related to the splitting of the d-orbitals. Only a certain wavelength is absorbed in the promotion of electron to a higher d-orbital and therefore the remaining colors are interpreted as a certain color. For example in copper(II) sulphate the red wavelength is absorbed and therefore it the complex appears to be cyan. But shouldn't the same amount of energy be released once the electron drops back to its previous state and releases the energy is gained? What wavelength would this drop correspond to?


texts: How does MP2 level of theory affect the natural orbital picture of the system?

texts: I have performed CASSCF calculations for a series of molecules with varying input orbitals. I have used UNO, UHF, ROHF and MP2 based natural orbitals to perform the CASSCF calculations. For my system I just wanted my input to be just pi-orbitals but the number of orbitals containing pi orbitals is different set of theory to form pi orbitals, with being less in number and least conjugated with MP2 based natural orbitals. When I am using MP2 based natural orbitals, the active space is turning out to be same for some molecules in the series. For example, I have an acene type of series and I am getting same active space say (8,8) for systems containing 6 benzene rings , 7 benzene rings and 8 benzene rings. Since the length of the system is increasing in a systematic fashion in terms of conjugation and the number of benzene rings, shouldn't the number of pi orbitals also increase in same manner ? But I am not able to see that, and therefore not able to justify the use of same active space for all. (For other cases like UNO, UHF the number of pi orbitals are increasing and also giving highly conjugated pi-orbitals in picture which is giving difficulty in convergence and for molecules big in the series exceeding the CASSCF limit.)


texts: Why can't calorimetry be used to measure fast reactions?

texts:
As my previous post was a bit unclear and unspecific, I am reformulating it. First of all this is a question that I had while reading some concepts my book introduces, so this isn't a homework question in anyway.

The context is: I have started reading the thermochemistry chapter of my book, it starts explaining the concept of heat and how a calorimeter works. After that, it shows the story behind Hess' Law and says that one of the reasons it was created is because a calorimeter can't be used to measure the enthalpy variation of too slow reactions, explosive reactions and too fast reactions. As a result, there was a need to create an indirect way of calculating the enthalpy variation, and this problem could be solved with Hess Law.

Now, I know why we can't use the calorimeter for too slow reactions and explosive reactions, but I would like to understand what is the problem with too fast reactions. Too fast reactions releases/absorbs heat on a small time period, but this shouldn't be a problem, because the calorimeter will get at equilibrium as other reactions.

As suggested, I am adding the paragraph of the textbook:

  As we saw, the heat involved in a transformation can be determined using a calorimeter. However, for many reasons, the calorimeter can't be used to determine the heat for every chemical reaction. There are situations where the reaction can be too slow or fast, can be explosive, it can even occur simultaneously with others undesirable reaction, what makes it impossible to measure the enthalpy variation for a specific reaction. How can we determine the heat involved in these type of transformations?

( I am brazilizan and the book is called Química: Cotidiano e Transformações)

So, what is the problem with too fast reactions?


texts: Heating p-Bromobenzenesulfonic acid in the presence of dilute HCl

texts:
How do I predict the outcome of this reaction?

I expected this to be an acid base reaction leading to the formation of the weak acid para-chlorobenzenesulfonic acid. However, the answer given in the worksheet was surprising $\ce{-SO3H}$ was eliminated and the product stated was $\ce{C6H5Br}$. I would like to be acquainted with the mechanism of this unusual  reaction. I couldn't find it in Clayden or Solomon Frhyle.


texts: When titrating to find the concentration of a dissolved acid, does the volume of solvent matter?

texts: I am conducting a titration to find the mass of aspirin present in tablets. I will be dissolving the aspirin tablet into a solution of ethanol and distilled water to dissolve it. But, does the volume of ethanol or distilled water added actually matter? Or does it just need to be enough to completely dissolve the aspirin?


texts: Find second acid dissociation constant at a given pH

texts:
In short, the problem states that:

  We have a molecule that has two ionizable groups
  $\mathrm{p}K_\mathrm{a,1}$ is between $5.0$ and $9.0$; $\mathrm{p}K_\mathrm{a,2}$ is outside of this range.
  $100\ \mathrm{mL}$ of a $0.1\ \mathrm{M}$ solution of molecule, all in the unprotonated form
  added $12\ \mathrm{mL}$ of $1\ \mathrm{M}\ \ce{HCl}$
  final $\mathrm{pH}$ is $7.4$

The goal is to find $\mathrm{p}K_\mathrm{a,1}$. This is how I've approached it:

First, I converted everything to moles:

$0.012\ \mathrm{mol}$ of $\ce{HCl}$ added $\ce{->} 0.012\ \mathrm{mol}\ [\ce{H+}]$
$0.01\ \mathrm{mol}$ of molecule in solution $\ce{->} 0.02\ \mathrm{mol}$ of $[\ce{A-}]$ since the problem states that everything is in unprotonated form I think this is were I am wrong in my thinking
Next, I reason that some $\ce{A-}$ is going to be neutralized by $\ce{H+ ->} 0.02-0.012$. Leaves me with $0.008\ \mathrm{mol}$ of $\ce{A-}$
Then, I have $0.012~\mathrm{mol}$ of $\ce{HA}$ that was formed.
Im plugging this in to the Henderson-Hasselbalch equation $\ce{->} \mathrm{pH} = \mathrm{p}K_\mathrm{a} + \log ([\ce{A-}]/[\ce{HA}]) \ce{->}$
leads to the incorrect answer.

I've tried looking at similar problems but I am just having a hard time with this. I feel that the problem lies with this the neutralization. Also, I know that upper boundary of $\mathrm{p}K_\mathrm{a,1}$ is $9$, which is above the final $\mathrm{pH}$, and I know that at $\mathrm{pH}=\mathrm{p}K_\mathrm{a} 50~\%$ would be protonated/unprotonated, however, I don't know how to account for this information in my calculation.


texts: Does Combining Solid/Liquid Concentration with $K_c$ Matter when Comparing $K_c$ of Different Reactions?

texts: I know it is convention to take liquid/solid concentrations as constants and lump it with the equilibrium constant. However, if we were trying to compare the equilibrium constants of two different reactions and if one of the reactions had a solid reactant, doesn't lumping the solid reactant concentration with the equilibrium constant make one reaction seem more product favoured than it actually is?


texts: Basic question about an expression for Gibbs free energy

texts:
I'm getting into thermodynamics, and I have a basic question about the following expression for Gibbs free energy:

$G = \sum \mu_i N_i$

Is it correct that this equality only holds for constant temperature and pressure, as follows from integration over N of the expression for $dG$:

$dG = -SdT + VdP + \sum \mu_i dN_i$


texts: What is the order of acidic strength among phenol, catechol, resorcinol and hydroquinone?

texts:
This question is from a book that gives the answer as

$$
\text{hydroquinone} < \text{resorcinol} < \text{phenol} < \text{catechol}
$$

but does not provide any explanation for the answer. If I go by the stability of the conjugate base due to resonance, phenol seems to have the most number of resonance intermediates and seems to be most stable. Considerations about number of resonance intermediates of conjugate base gives an order that is nowhere close to that provided as an answers.

Please provide an explanation as to the provided answer or, if the answer is wrong, please supply the correct order with explanation.


texts: According to Fajans' rules, greater charge in an ionic compound results in more covalent character. But why is it that sodium oxide is more covalent than magnesium oxide? Google says boiling point of magnesium oxide is more than sodium oxide.


texts:
I am doing a presentation regarding Stereochemistry, and I am a little confused with the terminology. My question is:

Are isomers and stereoisomers the same thing? Do they differ from each other?


texts: Calculating pH for titration of weak base with strong acid

texts:
Calculate the pH at the equivalence point for the titration of $\pu{0.130 M}$ methylamine ($\ce{CH3NH2}$) with $\pu{0.130 M}$ $\ce{HCl}$. The $K_\mathrm{b}$ of methylamine is ${5.0 \cdot 10^{–4}}$.

So I started with the equation:

$$\ce{HCl + CH3NH2 <=> CH3NH3+ + Cl-}$$

and then I knew that

$$\mathrm{pH} = \mathrm{p}K_\mathrm{a} + \log \left(\frac{\ce{[base]}}{\ce{[acid]}} \right)$$

So, I put ${\log \left(\frac{0.130}{0.130}\right) = \log 1 = 0}$ and then added that to the $\mathrm{p}K_\mathrm{a}$, which I got from the equation

$$\mathrm{p}K_\mathrm{a} = \frac{K_\mathrm{w}}{K_\mathrm{b}} \quad \rightarrow
 \quad \mathrm{p}K_\mathrm{a} = -\log(K_\mathrm{a})$$

However, after I plugged those in to get a $\mathrm{pH}$, it turned out to be wrong and then comments said that when titrated a weak base with a strong acid, the volume is doubled at equivalence point and the concentrations are halved.

Why is this? I now know that my original equation was wrong and it should be

$$\ce{CH3NH3+ <=> H+ + CH3NH2}$$

and from there I should make an ICE table with the concentration of $\pu{0.0650 M}$.


texts: Which compound can exist as stereoisomers?

texts:
I'm having trouble in understanding how to identify chemical compounds as stereoisomers.

In the question below, D is the correct answer according to the markscheme. I've drawn out the chemical structure but am unable to see what possible stereoisomers it can form.

I also tried visualising the possible isomers on Wolfram Alpha:

http://www.wolframalpha.com/input/?i=CH3CH2CHOHCH3

There are two isomers which stand out to me, which I guess are the stereoisomers?

(S)-(+)-2-butanol
(R)-2-butanol

However, to me it looks like they are just rotated versions of each other.


texts: Does intramolecular hydrogen bonding occur in dicarboxylic acids?

texts:
Consider ethanedioic acid:

Could it form intramolecular hydrogen bonds (between the C=O and HO)?


texts: Effect of nitro group basicity order of o,m and p nitroanilines?

texts:
Would someone please help me with this? The order of basicity of o,m and p nitroanilines is m>o>p. My book states that ortho isomer has -I effect, -M effect as well as ortho effect, and meta isomer has only -I effect while para isomer has -I and -M effect. These effects destabilize the conjugate acid.

My actual doubt is why exactly the nitro group has a negative mesomeric effect on ortho and para isomer, when actually it is a meta deactivator. Shouldn't it be having no effect at ortho and para positions, and destabilize the conjugate acid at meta position? I'm confused.


texts: Volume of sucrose (solute) contributing to volume of solution? (solvent = water)

texts:
I'm trying to make stock solution of 3M sucrose in water.  In 25ml, this is 25.672g sucrose (FW 342.3).  However, that mass of sucrose, in the powder, occupies a pretty substantial volume, such that if I add 25ml of water to it, I end up with a dissolved solution ~42ml in volume (it is fully dissolved).  Puzzled by this, I've also prepared a second solution in which I am only adding water up to the 25ml line in my 50ml conical (so far only 9ml).  This is obviously struggling to dissolve as the saturation solubility for sucrose is like 5M or something like that.

So what's the deal?  Is my 40ml solution with the correct mass of solute and volume of solvent really 3M?  My head says yes but my gut is uneasy.


texts: What is the result of this elimination reaction?

texts:
$$\ce{(R)-2-Bromooctane + alcoholic~KOH -> E2~reaction}$$

My answer is that this reaction will have a minor and a major product. In relation to the regiochemistry, the major product is the one which follows the Zaitsev rule, but this major product will still have two forms the trans- and the cis-, of course the major is the trans-. so there will be 3 different products.

Was I correct?


texts:
Many groups of bound atoms complexively bearing a (negative) charge are called complex anions. Examples are $\ce{NO3-}$, $\ce{CO3^2-}$, $\ce{BO3^2-}$, $\ce{CrO4^2-}$, $\ce{Cr2O7^2-}$, $\ce{MoO4^2-}$, $\ce{WO4^2-}$, $\ce{PO4^3-}$, $\ce{AsO4^3-}$, $\ce{VO4^3-}$ and the several, sometimes polymeric, complex anions occurring in silicate and borate minerals.

I apologise if I am asking something trivial, but I cannot find a source, except for silicates, for which I read that the $\ce{Si-O}$ bonds are basically covalent, explaining whether the bonds within complex anions are covalent in general.

Are they always covalent? If they are not covalent in general, are they in the examples I have written?


texts: Resonance contributors and IR stretching frequency

texts:
I am told that a carboxylic ester would have a higher carbonyl stretching wave number than a carboxylic amide due to there being more double bond character in the carbonyl group of the ester.

This makes sense prima facie; the resonance structures suggest that there is somewhat more double bond character in the carbonyl of the ester. And nitrogen and oxygen are nearly identical in mass.

Is this actually true and applicable?


texts: Why are there no chlorate esters? Or are they just undocumented or too unstable? I've seen perchlorate esters, but google "chlorate esters" and only perchlorate esters come up.


texts: Is there a chemical(s) that provides good discrimination between absorbance curves for different pHs in the UV light spectrum (100-400nm?)


texts: Nomenclature of alkenoic acids - which group has priority: the alkene or the acid?

texts:
Right, how do you systematically name them? Also, do you number them from the double bond end or the Carboxyl end?

Ie would it be something like.  2-methyl Hept-3-enoic acid?

Scuse the bad question and I made up the example, sorry! I'm really confused!

Thanks!!


texts:
I know some sulfur groups such as sulfones and disulfides and sulfonic acids. I also know of 1 phosphorus group. That is the phosphate ion.
I don't know of any boron groups.

What is the phosphorus equivalent of aldehydes, ketones, and carboxylic acids?

Phosphals, Phosphones, and Phosphonic acids I suppose?

And what about the boron equivalent of aldehydes, ketones, and carboxylic acids?


texts: Do electrons of opposite spin attract each other?

texts: Electrons of opposite spin create magnetic fields that are opposite to each other. So, is it possible that, 'such electron pairs attract each other' or ' they distract each other less than electron of same spin'? Thanks.


texts: Concentration and Half Life of reactants A and B

texts:
$3.12$ A reaction $\ce{A + B ->C}$, follows first order kinetics with respect to each reactant, with an overall rate constant $k=\pu{2.0 x 10^{-3} M-1s-1}$, the initial concentrations of A and B are $\pu{0.10 M}$ and $\pu{6.93 M}$. respectively. Given $\ln 2 = 0.693$, choose the correct statement(s).
(A) The concentration of A remaining after $100$ seconds is approximately $\pu{2.5 x 10^{-2} M}$.
(B) The concentration of B remaining after $100$ seconds is approximately $\pu{1.73 M}$.
(C) The half life for A is about $50$ seconds
(D) The half life for B is about $50$ seconds
Since reaction is first order with respect to both reactant A and B, I can write,

$$ k=\frac{1}{t} \ln{\frac{a}{a-x}}
 $$
where a is initial concentration of reactant and a-x is remaining concentration.
On solving the above for A and B after 100 seconds, I get $A_r = \frac{0.1}{e^{0.2}} $ and $B_r = 0.693/e^{0.2}$
The answer does not match with any options for both concentration as well as half life.
Can you please help me with this?


texts: In my quest for a non-electrochemical glyoxylic acid synthesis, I've found a few that seem simple and pretty OTC. The first is the reduction of oxalic acid with magnesium metal, which if I'm not mistaken forms a magnesium salt which is unwanted. The second is a mixture of nitric acid and ethyl alcohol, which I couldn't find any kind of yield and it was only briefly mentioned in a patent. The third is the oxidation of a glyoxal solution with nitric acid and again I couldn't find any info on reaction time, yields, and whatnot. Has anyone tried any of these methods with reasonable results?


texts: Finding direction of the reaction using Affinity of the reaction

texts:
I encountered following reaction:

$$\ce{CO + 1/2 O2 -> CO2}$$

I am provided with the composition of the various gases at $\pu{1000K}$ and am asked the direction of the reaction by finding the affinity of the reaction. I know the way to find affinity is:

$$A= \mu_\ce{CO2}-\mu_\ce{CO} -\frac{1}{2}\mu_\ce{O2}$$

I know the change in chemical potential considering ideal mixing. But how do I go about finding the absolute value of chemical potential, rather than the change, because the expression requires the chemical potential itself rather than the change? I thought of writing $A$ as $-\Delta G$, but for that also I need some reference value of $G$ and from there I can integrate $\Delta H-T\Delta S$, but again I can't figure out how reference state is chosen?

Please suggest something.


texts: derivation of partial differential equations for changes in U

texts:
Changes in internal energy at

  At constant temperature, $$d U = \left({\partial U \over \partial V}\right)_TdV$$
  At constant volume,
  $$d U = \left({\partial U \over \partial T}\right)_VdT$$
  When both temperature and volume is changing,
  $$d U = \left({\partial U \over \partial V}\right)_TdV +\left({\partial U \over \partial T}\right)_VdT$$

    I want to know how do we get these equations.

I think I can speculate a bit about how do we get the first and second equation.

For the first equation, since the temperature is kept constant, we can plot a U-V graph.

Tell me if I am wrong here but for that graph the slope at a given point is $\displaystyle \left({\partial U \over \partial V}\right)_T$.

Now since the change is a infinitesimal change, the slope of tangent at that point is given by $\displaystyle \left({\partial U \over \partial V}\right)_T$.

So $\displaystyle {\Delta U \over \Delta V} = \left({\partial U \over \partial V}\right)_T$, since the change is infinitesimal, $\Delta U = dU, \Delta V = dV$ and substituting this we will get out equation 1. Same can be said for equation 2.

I have no idea how do we get the equation 3, I think it is a clever use of  product rule or something like that.

Is my understanding for the equations 1 and 2 correct ?
How do we get equation 3 from 1 and 2 ? because simply adding 1 and 2 does only give the RHS of 3 not the LHS.


texts: Does bicyclo[3.2.0]heptane have a plane of symmetry?

texts:
Most stable form of cyclobutane is the "envelope form" and most stable
  conformation of cyclopentane is either the "envelope form" or the "twist"
  form.

In the above compound do the individual rings exist in their most stable conformation? Or is the actual situation different?
What is the most stable conformation of the above compound? And does it have a plane of symmetry?


texts: Why is Ionization Energy definition restricted to gaseous atoms?

texts:
Here's the definition of ionization energy that I am learning at this level:

  energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of uni positively charged gaseous ions.

I would like to know, why did they specify that the removal of electrons have to be at gaseous state and the ions that form are gaseous as well? Does it have to do with the amount of energy supplied that causes the elements to vapourize?


texts: Is it possible to store moist air at high pressure?

texts:
Is there any way to store moist air inside a high pressure tank?
Let's suppose that I have humid air (30%) at room temperature and I want to store it at 300Bar in a tank. when I extract the fluid from the tank (isothermal expansion) to bring it back to ambient pressure will I keep the same percentage of humidity?
In most cases where it is necessary to store high pressure air to be used in a system that requires humid air, a cylinder is used where ambient air is stored which then pass into a humidifier. I'd like to know if it is possible, conceptually, to remove the humidifier and directly store moist air in some way


texts:
I need to do molecular dynamics simulation of cyclodextrine molecules for a project and I am searching for an open source solution that can be used. I found LAMMPS to be quite well maintained and wanted to use it for the MD simulation. However, after spending now around 10 hours trying to figure out how to specify an input geometry for a LAMMPS calculation, I am stuck. Has anyone experience with doing MD simulations of molecules using LAMMPS?
Given an input structure in standard .xyz format, how do I start a LAMMPS MD calculation on it?


texts: What order would these compounds elute in a 3:1 hexanes:ethyl acetate TLC run?

texts: I would figure the order would be (in order of smallest Rf to largest) W, Z, Y, X. Is the carboxylic acid more polar than the acetic anhydride?


texts:
Tert-butyl alcohol seems unusual among alcohols in that its melting point is high (25°C) while its boiling point is also still low (82°C).  I am looking for more materials with phase-unstable liquid regions like this so I'm curious what makes the liquid phase so unstable relative to the solid and gas phases?

Do the methyl groups align and act like alkanes to stabilize the solid but the molecule is still small enough to have a low boiling point?

To my larger point, any advice on characteristics of materials that exhibit low liquid phase stability?


texts: What properties a compound should have to be called an "ice"?

texts:
I wonder what compounds are usually called "ice" and what properties do determine it?

I can bring some examples of ice and not.

Not ice:

$\ce{H2S}$
cellulose
sugar
graphite
lithium
solid mercury
polyvinylchloride
solid fats
...

Known as ices:

solid water
solid $\ce{CO2}$
solid nitrogen
solid oxygen
solid methane (?)
solid ethanol (?)

It seems they all have some common properties:

Melting point below room temperature
Transparency
White or blueish color
Chystalline structure (?)
Easy sublimation and high saturation pressure
Low strength and other mechanic properties
Low surface friction (?)

Have I missed anything? What is the accepted definition of ices, say in astronomy or chemistry?


texts: Difference between "physical quantities" and "units"?

texts:
My textbook, Atkins' Physical Chemistry, 11th edition, by Atkins, de Paula, and Keeler, says the following:

  Although it is good practice to use only SI units, there will be occasions where accepted practice is so deeply rooted that physical quantities are expressed using other, non-SI units. By international convention, all physical quantities are represented by oblique (sloping) letters (for instance, $m$ for mass); units are given in roman (upright) letters (for instance m for metre).

I'm confused about what the difference here is between "physical quantities" and "units"?

I would appreciate it if people would please take the time to clarify this.


texts: C + O2 is equal to C + O, how is that possible

texts:
C + O = CO2 . This is because carbon has valency of 4 while oxygen has valency of 2. When they react the valencies are criss crossed which means we will get C2O4 but this is simplified to CO2.

But my textbook say that C + O2 = CO2.

So how is it possible that C + O2 and C + O both get the same product of CO2?

Also you can say that the reaction of C + O = CO2 is not balanced but the balanced chemical reaction would be C + 2O = CO2 not C + O2 = CO2 which is the reaction that my textbook says.


texts:
What is the radius of the hydride $(\ce{H-})$ ion? There are several sources with conflicting reports on the same.

Inorganic Chemistry: Principles of structure and Reactivity cites Pauling’s 1960 study of the hydride ion, stating that

  it has a radius of 208 pm compared to 216 pm for the iodide ion

This would imply that it is larger than the fluoride, chloride and even the bromide ion! This article in nature disproves the above and states:

  the ionic radius of an $\ce{H-}$ ion is 134±2 pm, which is slightly larger than the radius of $\ce{F^-(II)}$ (128.5 pm) and almost the same as the radius of $\ce{O^2-(II)}$ (135 pm). This evaluation agrees with the generally accepted trend that the radius of an $\ce{H-}$ ion is nearly the same or slightly larger than that of an $\ce{F-}$ ion.

Which one of these is correct? Also, could additional citations be given to tell the exact size of the hydride ion?


texts: Why do we need to incubate this system for 18 hours at 60 degrees Celsius?

texts:
I am conducting a bio-chemistry related experiment and I have been unable to understand a step which is commonly performed. The procedure that is confusing me is outlined in the supporting information, beginning on page S2.

My aim in this step is to apply a PEG (Polyethylene glycol) silane layer.

After immersing ITO (Indium Tin Oxide) slides in a PEG-concentration, the slides are incubated for 18 hours at a temperature of 60 degrees Celsius.

Can you tell me why the incubation is performed? And why is it for 18 hours at 60 degrees Celsius?


texts:
I am reading Dan Broughton's answer in replying to the question "why does the gas from dry ice flow down" here.

According to the answer, the fog is water's color and water is condensed and suspended in the CO2.
Do you agree with this answer? If so then should water have color? I see some documents saying that it is nearly colorless.

  Why does the gas from dry ice flow down?

  Dry ice is simply the common term used for solid carbon dioxide (CO2),
  so the gas coming off of the dry ice is CO2 gas. CO2 gas has a density
  of 1.96 kg/m^3 and air (78% N, 21% O2) is 1.29 kg/m^3. Since the CO2
  is more dense, it sinks in air.

  But CO2 is colorless, so what makes it appear as a white mist? As the
  gas sublimes (change directly from solid to gas), it comes off of the
  dry ice at -78.5 C (-109.2 F).  Being well below the freezing point of
  water, any moisture in the air surrounding the dry ice condenses and
  is suspended in the CO2, creating the cloud/fog effect that we can
  see.

  These two phenomena combined are what create the fog that flows along
  the ground.


texts:
Need some help from chemists.

All questions are hypothetical situations, I am not trying to synthesize this chemical.
I am trying to understand its formation and reactions,
And if certain chemical reactions could accidentally generate methyl mercury compounds.

Wanted to know the possibility of Dimethyl Mercury formation when carrying out O-Methylation reactions in dirty AL/Hg contaminated glassware.
Could the Methylating reagent Dimethyl Carbonate, with DBU as the catalyst generate Dimethyl Mercury in such glassware?
Could Dimethyl Mercury be synthesized by direct action of Dimethyl Sulfate on Mercury metal?
Or must it be used with Na/Hg amalgam?
Also could Na/Hg be treated with Ethyl Bromide to form Diethyl Mercury?
Or is only Ethyl Iodide strong enough to work?

Thanks for the help!


texts:
I came across the following compound syn acetaldoxime
However why is it syn because the lone pair having lowest priority is anti to H which is lowest priority on other side.
Please clarify


texts:
A student investigated the volume of sulfuric acid that reacted with 25 cm3 sodium hydroxide. Describe a titration method the student could use in this investigation. {6 marks}

My answer:

Use the pipette and pipette filler to safely add 25 cm3 of $\ce{NaOH}$ to a clean conical flask.
Add a few drops of indicator and put the conical flask on a white tile (so you can see the colour of the indicator more easily).
Fill the burette with $\ce{H2SO4}$ and note the starting volume (record from bottom of the meniscus at eye level).
Slowly add the acid from the burette to the alkali in the conical flask dropwise, swirling to mix.
Stop adding the acid when the end-point is reached (the appropriate colour change in the indicator happens). Note the final volume reading of $\ce{H2SO4}$ (record from the bottom of the meniscus at eye-level).
Repeat steps 1 to 5 until you get consistent readings

Have I missed anything that will prevent me from getting 6 marks?


texts: Do only outer electron shells take part in forming chemical bonds? Or could an inner shell create a bond under some conditions?


texts:
How do you know when to name a benzene ring substituted by a simple haloalkane as a derivative of benzene or as a derivative of the alkyl halide.

For example, is it 1-chloro-4-isopropylbenzene or 2-(4-chlorophenyl)propane?


texts: Order of molecular mass of solvent; given boiling point

texts:
Given three solvents X, Y, Z. Order of boiling point of pure solvent X < Y < Z and same order of molal elevation constant ($K_\mathrm{b}$). Find the order of molecular mass.

So I got this question in my tuition test and the solution is unclear. This question is troubling me a lot.


texts:
Why is 15,16 dihydropyrene aromatic?

Here the middle two carbons are $\ce{sp^3}$ hybridized. Then how is it aromatic? Do we only consider the conditions for aromaticity to apply only at periphery in case of fused rings?


texts: Which salts can be used to precipitate chloride ions?

texts:
We don’t have AgNO3 in the lab. I have no idea what else can be useful.
I am washing a product and I want to make sure the chlorides are washed away.


texts: What is "stuffy"/"stale" air composed of?

texts:
When a room is not ventilated for a long time (days if people are present, weeks if not), humans perceive a change in air quality commonly described as "stale" or "stuffy" air.

What is going on here chemically? How is "stale" air different from normal air?

Note that the difference cannot be the mere presence of biological exhalations from the inhabitants, as the phenomenon definitely also occurs when nobody lives in the building at all (though it takes a lot longer in that case).


texts: How do breaking chemical bonds turn into kinetic energy

texts:
I’m trying to understand how breaking chemical bonds turn into kinetic energy. If AB is a chemical which breaks into A and B which zip away from each other, is it because when the bond breaks they suddenly repel each other? Another way I'm thinking of this is what happens if one single molecule of AB alone in a vacuum breaks apart.

I think the point I'm trying to make is the reaction is making the products move faster than when they started. It takes a force to make things move. So it has to be either gravity, electric, magnetic, or one of the nuclear. I'm pretty sure we can rule out nuclear and gravity.


texts: Why do some crystal structure files not include bonds?

texts:
Why do some crystal structure files not include bonds (the atoms are just placed in the respective position in the cell without bonds between any atoms)?
Shouldn't the bonds always be there?
Also, where can I look up these bonds?


texts: dsp3 and sp3d hybridization — what is the difference and which applies to square pyramidal?

texts:
What is the difference between $\mathrm{dsp^3}$ and $\mathrm{sp^3d}$ hybridization?
Are they one in the same?

Also, I have a book that says that in compounds where the central atom is $\mathrm{dsp^3}$ hybridized, it's shape is square pyramidal, like that of $\ce{BrF5},$ but the hybridization of $\ce{Br}$ in $\ce{BrF5}$ is $\mathrm{sp^3d^2}.$ Why is it so? Is my book wrong or am I missing something?


texts:
Please, I have a question here as a non chemist:

Is it true to say that as of 2020, chemists can create any gemstone, from 1 to 10 level of Mohs' Scale strengths, artificially?

If so, please detail if it causes any serious financial damages to the "old school" gemstone industry of picking and mining and polishing gemstones from natural environments and deposits respectively, or if the two industries keep thriving one alongside the other.


texts: Hydration, Coordinate Bonding, and Reduction Potential in Groups 1 and 2 Elements

texts:
Whenever an alkali metal such as Lithium is hydrated/solvated, coordinate bonding occurs and it is the high hydration enthalpy of lithium which makes it the strongest reducing agent in aqueous solution. My question is, if lithium is hydrated and becomes surrounded by water molecules in coordinate bonding, then how does the overall reaction of adding lithium to water produce LiOH and H2(gas) ?  Is the coordinated ion an intermediate product?

I also am wondering what happens to the "lost" electrons from the metal in coordinate bonding.  Take Beryllium dissolving in water as an example. As it is hydrated it will lose the 2 valence electrons in its outer orbital and then it hybridizes its orbitals into 4 empty orbitals so that 4 molecules of water, supplying 1 lone pair each, can bond with the positive beryllium ion. Where did the original 2 electrons go?  How do these electrons vanish in order to allow the hybridization of the 4 empty orbitals for water molecules to bond with?

And if Lithium is the strongest reducing agent in aqueous solution I assume it means it is reducing water itself, in order to create lithium hydroxide and hydrogen gas, but again, how does that come about from the coordinate bonding and the hydrated lithium? Coordinate bonds preserve the charge of the cation but I am not quite sure how this is so.

I have included an image below from a website that attempts to explain it, but I am confused about to where the original electrons go.

The website from which I took the image is:  https://www.chemguide.co.uk/inorganic/group2/beryllium.html#top


texts:
How can we find the order of percentage of enol form
of the compounds in the following equilibria?

Percentage of enol form in x is highest as due to aromaticity. But how can we compare that for y and z. The compound z is non-aromatic but compound y has resonance.


texts: Table of expanded electronic structures of atoms

texts:
Where can I find the table containing expanded electronic configurations for atoms in the periodic table, showing how outer electrons are distributed between different atomic orbitals?

I really just need to know the expanded electronic configurations of sulfur S and tungsten W.

So, for sulfur, amongst others, there are $p_x%$, $p_y$, $p_z$ atomic orbitals. And for tungsten W, amongst others, there are $d_{xy}, d_{xz}, d_{yx}, d_{x^2-y^2}, d_{z^2}$ atomic orbitals. I need to know how exactly electrons are distributed.

Does anyone have any idea where I can find the information or how I can derive it?


texts: Decreasing order of electron density in benzene ring among the halobenzenes

texts:
What should be the order of electron density in monosubstituted halogen derivatives of benzene?
I am aware that fluorobenzene is more ring activating as compared to chlorobenzene due to the more effective +M effect of F over Cl, but I would like to know the full order among all the monohalogenated benzene compounds.
Is there any significant +M effect shown by Br, I with the benzene ring?
If yes, then how strong is it as compared to their –I effect?
Please let me know the correct final order of electron density in the benzene ring among Ph—F, Ph—Cl, Ph—Br, Ph—I, as well.


texts: How many moles of the substance are in 2.5 g of lead?

texts:
How many moles of the substance are in 2.50 g of lead?

What I did:

Atomic mass of Pb: 207.2 amu (or g?)

Applying unitary method, 1 mol of Pb -> 207.2 g; so, x -> 2.5 g

$x = \frac{2.5}{207.2}= \pu{0.0121 mol}~\text{of}~\ce{Pb}$

Shouldn't it be like this?:

1 mol of Pb -> $(\pu{207.2 amu} \times1.66\times(10^{-24}))~\pu{g}$ so x -> $\pu{2.5 g}$


texts: Understanding three-dimensional structure of common salt

texts:
I started reading through The Feynman Lectures and came across this diagram. What do the numbers next to the nodes in the diagram represent? It's not explained in the text. All that is mentioned is: "Figure 1–7 is an illustration of the three-dimensional structure of common salt, sodium chloride."

A direct link to the text is here, just Ctrl-F "crystal of salt".


texts: Why are entries missing on a solubility data chart for ionic compounds?

texts:
There is a solubility chart in my college chemistry class text for "Solubility of Ionic compounds in water". I have copied and pasted image of chart below.  I was surprised to find a dozen ionic compounds marked "--" meaning "no data".

Among the entries marked "no data" are

iron(III) iodide
iron(III) sulfide
iron(III) carbonate
iron(II) chromate
copper(II) iodide
magnesium chromate
silver hydroxide
and carbonate, chromate, and nitrate for Sn2+

It's hard to believe there is no solubility data on said ionic compounds. They should be either soluble, insoluble, slightly soluble, or an impossible compound.  I asked my professor, and he said most of said compounds are too unstable to get reliable solubility data.  In other words, the said cations and anions would not form a stable ionic compound long enough to test solubility.  He also said it might not be the case for all the "--" no data compounds. Which of the said "no data" compounds are impossible compounds as distinguished from possible stable ionic compounds for which there is really no solubility data?


texts: Why are enynes named as -en-yne and not -yn-ene?

texts:
The preferred IUPAC name for the compound above is hept-1-en-6-yne. I understand that the numbers are chosen in order to give the alkene the lower locant, as explained in Should double or triple bonds have preference for low locants in IUPAC nomenclature?.

However, I'm wondering why the name has the form -en-yne instead of -yn-ene. In other words, why is it not "hept-6-yn-1-ene" instead?

Furthermore, if this is an IUPAC specification, is there any rationale for why en-yne should be preferred to yn-ene?


texts: Diluting acetic acid to obtain a solution of pH 5

texts: What percent of a solution needs to be acetic acid for a particular $\mathrm{pH}$?  I have 100% acetic acid, and want $1~\mathrm{L}$ of solution with a $\mathrm{pH}$ of 5. I've done some research, but I still do not understand how to solve this problem.


texts: Could any constituent of normal human urine produce a false positive in a Kastle-Meyer test for presence of blood?

texts:
From my understanding, one forensic test for the presence of traces of blood at a crime scene is (or was) the Kastle-Meyer test. Doing some research, I understand that in the test, hemoglobin reacts with hydrogen peroxide which oxidizes phenolphthalin into phenolphthalein which then changes it's colour to bright pink.

My question is, are there any constituents of normal urine that could cause a false positive in this test?

To be clear, my interest is academic, not personal.


texts: Can carbon be the central atom of a complex? Can it form a quadruple bond with itself?

texts:
Why does $\ce{[C(NH3)2]}$ not exist as a complex? Here, $\ce{C}$ is carbon and the configuration of $\ce{C}$ in ground state is $\ce{[He] 2s^2  2p^2}$.

Can't the two $\ce{NH3}$ molecules pair the two $\ce{p}$ electrons of carbon and form coordinate bond with carbon?

Why does $\ce{C2}$ (one carbon atom bonded with other through quadruple bonds) not exist? Two $\ce{2p}$ orbitals of $\ce{C}$ should form π bonds and one $\ce{2p}$ and one $\ce{2s}$ should form σ bonds with the other $\ce{C}$ (without hybridisation).

I'd appreciate an answer for a beginner.


texts: Is there an otherwise liquid material that has angle of repose?

texts: I wonder whether there is a material which consists from individual molecules (that is, fluid), which has its angle of repose thus exhibiting propertes of a powder?


texts: What factors other than Gibbs free energy determine formation of a compound?

texts: The $\Delta G_{f}^{\circ}$ value for $\ce{Fe2O3}$ is less negative than that of $\ce{Fe3O4}$ in JANAF table at room temperature but still, $\ce{Fe2O3}$ is what's formed. How does one explain this given that it's not the thermodynamically favored one?


texts: What gives rise to the color of sapphires?

texts:
Here is what I know:

Sapphires are composed primarily of $\ce{Al2O3}$ (in pure form colorless) as well as Fe and Ti (trace impurities responsible for the color). I know that the proportion and identity of trace elements gives rise to various colors but I just want to focus on the combination that gives blue right now.

The explanation that I could find online says that the reason we see blue is because of intervalence charge transfer between the iron and titanium ions. Specifically Ti(IV), Ti(III), Fe(III), and Fe(II) are involved. The ground state configuration is controversial but is presumed to be both ions in their 3+ state. It could also be Ti(IV)-Fe(II). The first part of my question is what is the exact equation for the process occurring? I could not find a redox potential for the reaction $\ce{Ti(IV) + e^- -> Ti(III)}$ so I'm not sure which direction the electrons flow. The half reaction $\ce{Fe(III) + e^- -> Fe(II)}$ has a positive reduction potential of +0.77 V. I assumed that a photon provides enough energy for the fourth ionization energy of Ti (4174.65 kJ/mol) and that electron is transferred to Fe(III). I don't think this can be correct though because that energy would be in the ultraviolet region on the J/atom scale. This is the same for the third ionization energy of Fe. I was expecting to see something closer to yellow light region ~575nm. So from this its clear that I'm probably missing the idea regarding the physics occurring here.

The second part of my question has to deal with color subtraction in general. Why does a sapphires absorption of yellow light lead to blue color in the first place? I've seen an explanation that you imagine white light as a mixture of only the primary colors red, blue, and green light. Also its stated that the secondary colors are formed as follows: red + green = yellow, blue + green = cyan, and red+ blue = magenta. Then if a sample absorbs for example yellow light (R+G) then only blue light remains from the original R+G+B=W combination. This makes sense at face value for me but I wanted to go a bit further. I assume the origin of this color addition and subtraction theory is that humans have cones specific for detection of red, blue, and green light (with a range of wavelengths of course to cover the whole spectrum). My difficulty with the color subtraction answer for the color origin is the fact that our cones detect a range of wavelengths. If the sapphire only removes a single wavelength of light close to 575nm (yellow), how is the effect so dramatic to make the stone blue? Won't the stimulation of the cones not have changed dramatically?

Feel free to answer as in depth as possible! Thanks-


texts: (Probabilistic) entropy associated with many equally probable microstates

texts:
This is a pretty naive question. The probabilistic definition of entropy is (for a mole of particles)
$$-R\sum_i p_i\ln p_i $$ in which $p_i$ is the probability of a given microstate and $\sum p_i =1, p_i\geq 0.$
If we have a large system whose microstates are equally probable the terms of $-R\sum p\ln p$ will trace a curve like that below (image on Wolfram Alpha), the area under which is (up to some multiplicative constant, omitting R) $ A=0.25.$

My question is whether there is any physical intuition or significance to the shape of the curve. In particular, why would the entropy associated with identically probable  microstates not be the same?
In case it sharpens the question, I would expect that as we add up entropy associated with equal-probability microstates the entropy would accumulate in a linear way. That is evidently not the case.
Thanks for any insights.


texts: Formation of thermodynamic product from 1,4-addition

texts:
Question:

The temperature is high enough for formation of the thermodynamic product. Now, there are two possibilities:

Starting with the top double bond

2

Or, starting from the bottom double bond,

The answer given specifies that the second product is formed. Why is this, why isn't the first product formed?


texts:
We have national elections coming up in two days, and like every time the election officials will mark people's thumbs with a dab of some purple solution that leaves a brown stain on the skin (and thumbnail) that takes a while to grow out. I'm pretty sure that's a potassium permanganate solution - that stuff behaves exactly the same.

Now I'm not into electoral fraud (there are other controls in any case) but I dislike having that stain on my fingernail for a month or more afterward. Previously I've had partial success by rubbing butter into my skin, but the stain still gets through. I've also tried making some plain old sugar or even glucose available, hoping that it would get oxidized first, but I can't conclusively say that that worked.

Any other tricks to avoid, or at least strongly mitigate, these stains? There's a window of about a minute or two where the purple solution sits on the cuticle while I'm unable to do anything about it.


texts: Short Cut Method to Calculating pH of Polyprotic Acid?

texts:
I am doing the following question:

  Calculate the pH of a $4.00\ \mathrm{mol\ L^{-1}}$ solution of citric acid.
  $\mathrm{pK_{a1}} = 3.09~~~~~ \mathrm{pK_{a2}} = 4.75~~~~~ \mathrm{pK_{a3}} = 6.40$

Usually for polyprotic acids, we can assume that the second, third and other dissociations  of $\ce{H+}$ ions are negligible when compared to the first dissociation. However I believe that this is only valid when the pKa values are separated by around 4. So for citric acid, this would be an invalid assumption as the pKa values are pretty close to each other.

Now, I can find the pH of the solution by doing the long way by first finding the amount of $\ce{H+}$ ions formed by the first dissociation, then using that to find the amount of $\ce{H+}$ ions formed by the second dissociation and so on.

However the room that they have given for this question is pretty small and has only has enough room for a couple of lines of working out and I definitely wouldn't be able to fit all my working out in that box.

So am I missing some short cut method to finding the pH in cases like this, or is the above assumption that I have outline at the start still correct for citric acid?


texts: What's the difference between mass spectrometry, mass spectroscopy, and mass spectrography?

texts: It seems that the terms mass spectrometry, mass spectroscopy, and mass spectrography are mostly used like synonyms. Is this correct? Or is there a difference?


texts: Geometry optimization of a small molecule inside of a larger one

texts:
I'm very new to this and trying to optimize the structure of a larger molecule that "wraps" around a smaller molecule. I'm using ORCA. I'm having two issues with the task:

a) I've attempted to use the following:
! RI BP86 def2-SVP def2-SVP/J D3BJ TIGHTSCF Opt Grid3 FinalGrid5
but have not had any success.

b) How can I reliably export a two-molecule starting configuration in .xyz format starting from ChemDraw? I've tried exporting in .cml, loading in JMOL/Avogadro/Molekel and printing in xyz, but it invariably destroys the bonds.


texts: Absorbance vs titrant added in acid-base titration

texts:
I was working on this question:

  Nitrophenol is a colorless weak monoprotic acid
  ($\mathrm{p}K_\mathrm{a} = 7.2$) whose conjugate base is bright yellow. To
  $2.00\ \mathrm{mL}$ of a solution of $\mathrm{0.0100\ M}$ nitrophenol is added
  $\mathrm{1.00\ M} ~\ce{NaOH}$ in $\mathrm{0.001\ mL}$ portions, and the absorbance
  of the solution at $\mathrm{485\ nm}$ is monitored. What does the
  graph of $A_\mathrm{{485}}$ as a function of added volume of $\ce{NaOH}$
  look like?

The answers given were:

My reasoning for this question was that the absorbance is proportional to the concentration of conjugate base present in the solution. As the titration progressed towards the equivalence point ($\mathrm{0.02\ mL}~\ce{NaOH}$ added), the concentration of base increased. Then, as more base is added beyond the equivalence point, the concentration of base decreased, since no more base is being produced but the solution is being diluted. Therefore, I thought the correct graph was (A). However, the correct answer ended up being (B). So why would the concentration of base stay constant past the equivalence point?


texts: Zinc Picolinate - Positive, negative or neutral charge?

texts:
I'm going to be using a finings agent with a positive charge to remove negative trub from a solution (beer).

I would like to keep some chelated zinc in the solution - ideally zinc picolinate - so wondering what its charge is? I'm hoping it's neutral...

Depending on the answer, are there any zinc chelates that carry a neutral charge?

It's all so zinc can remain in the beer after fining to reduce the estrogenic effects of hops.


texts: Which resonance structure to use for writing curved arrow mechanisms?

texts: If a structure with delocalized electrons participates in a reaction, which resonating structure do you use to write down the mechanism? Is using either equivalent? Is it preferred to use the resonance hybrid? If so, what are the rules of using curved arrows for partial bonds?


texts: Why does nitric acid have a different molecular structure from phosphoric and arsenic acids?

texts:
I remember that this really bugged me as an undergrad, and upon revisiting some inorganic chemistry notes I realized I still don't have a satisfactory answer for it. The structure of nitric acid, $\ce{HNO3}$, is quite different from the structure of phosphoric acid, $\ce{H3PO4}$ and arsenic acid, $\ce{H3AsO4}$:

Something tells me there should be an easy, intuitive argument explaining this, perhaps something about p-orbitals being more diffuse in phosphorus and arsenic? I find it kind of difficult to analyze this as a sort of "trend", since other groups don't really seem to have well defined oxyacids for the first two or three elements.

There is no oxyacid for water, but sulphuric and selenic acids are similar in structure; there is no oxyacid for fluorine either, but the oxyacids of chlorine and bromine are also analogous. In the carbon group something kind of strange also happens, with silicic acid (I believe) not really being a well-defined compound but a plethora of different things with different relative stabilities.


texts: What is the optical nature of the tris(ethylenediamine)cobalt(III) cation?

texts:
The molecule I've drawn has neither a plane of symmetry nor a center of symmetry, even though some books refer to this as optically inactive.

Can you please elaborate why is this so, or those books are wrong.


texts: Why is cupric oxide more basic than cuprous oxide?

texts: I have learnt earlier that metal oxides with higher metal oxidation states are more acidic than those with less oxidation states, but copper disobeys this rule. Why?


texts: Electrolysis of calcium hydroxide in glycerol

texts: Calcium hydroxide is soluble in glycerol. Assuming anhydrous conditions, could such a solution be electrolysed to yield calcium metal, or would glycerol OH groups interefere with the process?


texts: Is there a soluble salt, or compound that when dissolved in water results in a solution with density less than pure water?

texts:
Generally water soluble salts tend to 'fit between' the molecules of water such that the volume of the resulting solution does not increase much relative to the volume and added mass of the salt. So the result is that the solution generally has a higher density than pure water.

But are there any special cases; any salts or compounds that result in an expansion of the resulting solution volume such that its density actually decreases?

Sodium polyacrylate comes to mind, but if I'm not mistaken, the expansion doesn't take place until a significant amount of the compound is added, and then only after the liquid is changed to rather a gel or solid. My question relates to the resulting solution actually being a liquid with density < 1.0 g/cm³.

So then if not for water, are there solutions of other solvents that might behave this way?


texts: When Z>1 are repulsive forces dominant or are attractive forces dominant?

texts:
According to PVreal = ZRT

If z >1 repulsive forces are dominant or are attractive forces?
Different teachers are telling contradictory answers and after referring a few books, I have become more confused.

Points for ATTRACTIVE FORCES are dominant:

At high pressure the molecules do not strike the walls with full impact as they are dragged back by attractive forces.
When molecules are farther away from each other(as Vreal > Videal) the attractive forces are dominant.
Repulsive force are dominant when he molecules are almost in contact .

Points for REPULSIVE FORCES are dominant:

At high pressure the molecules are close each other that attractive forces are negligible but molecular size is significant.Thus repulsive forces are significant
As volume of real gas is more than volume of ideal gas , the real gas is more difficult to compress.Thus repulsive forces are dominating.

There was a question where P = 12atm T = 350K and Z = 1.2(after calculation). It was given that repulsive force are dominant.But my teacher said it was wrong and it should be attractive forces.


texts:
I have been studying flash distillation, and I am reading the VLE tables my textbook has provided.
I am looking at these tables and I am not understanding the data, I think.

Why is the vapour mole percent ($y_{benzene}$) and liquid mole percent of benzene ($x_{benzene}$) zero at 110.62 $^0 C$? Does that mean benzene just disappear from the flash distiller at that temperature?


texts: Can you predict the resistance of conjugated polymers as a function of degree of polymerization (DP)?

texts: Electrical properties of very simple systems can be calculated using NEGF. Is there a way to calculate the resistance (and other electrical properties) of a conjugated polymer, as a function of degree of polymerization (DP)?


texts: PdPS is being considered as a layered material but when I look at its crystal structure it does not look like that. Fo example I could not figure out its interlayer distance. Does anyone familiar with this structure?


texts: Can the eigenvalue for a quantum mechanical operator be zero?


texts: Cracking of dicyclopentadiene - was my simple Liebig condenser distillation setup adequate?

texts:
I recently did a distillation of dicyclopentadiene (bp 166 °C) to get cyclopentadiene (bp 40 °C). The setup as instructed by my supervisor consisted of a simple water-cooled Liebig condenser. Oil bath temp. at 180 °C, receiving flask held at -78 °C by a dry ice-acetone bath:

Everything seemed to work fine, and I got plenty of cyclopentadiene after distilling for about 4 hours.

Now (writing the report) I went hunting for some procedure references, and the first hit was this one (http://www.orgsyn.org/demo.aspx?prep=CV4P0238):

My interpretation of these instructions look like this:

My questions (too many I know, sorry):

Is my interpretation of that setup correct?
What is the Friedrichs condenser for?
Why should the water temp. be 50 °C? (and how important is it to get this temp. correct?)
Where would I attach the "calcium chloride drying tube" and what is it anyway, what's it for and how important is it to have one?
Other procedures I found attached Nitrogen to the setup. Why would I do that and how important is it?
How would you interpret "efficient water-cooled condenser"?
Finally, can you put me at ease and tell me that my simple distillation setup was just fine?


texts: What is the proper Lewis structure for HCOOH?

texts:
I tried to draw the Lewis structure of $\ce{HCOOH}$ but I didn't get the correct representation.

As you can see in the picture below, at no. 1, I put $\ce{C}$ as the central atom because it has less electronegativity than $\ce{O}$ ($\ce{H}$ cannot be a central atom). I drew the structure, but it is wrong because it violates the octet rule.

Then I came up with another structure as shown at no. 2,
and it seemed correct to me, but when I searched on Google for the correct structure, I found out that I am wrong.

Why is the structure that I drew in no. 2  wrong, even though the formal charges are zero?

How do I figure out the correct order of atoms in such molecules like the one above. What I mean is how do I know that the $\ce{C}$ will have $\ce{H}$ on the left and one $\ce{O}$ up and $\ce{O, H}$ on the  right side?


texts: What is the type of dependence of the rate of reaction on the amount of catalyst?

texts:
I have performed an experiment where I had some test tubes with the reagents and different amounts of catalyst. I started the reactions and measured the time they took.

Then I calculated the rate of reaction and plotted it in function of the amount of catalyst (in mL) in each test tube.

However I can't decide between a logarithmic fit line and a linear one (though the logarithmic one has a higher $R^{2}$). The data points are below.

If it helps, the reaction we used was the one of potassium permanganate with oxalic acid. We also added sulfuric acid and the catalyst used was manganese sulphate.

What would make more sense?

0   4e-05

0.2 7.22e-05

0.4 0.000136

0.6 0.000159

0.8    0.000183

1    0.0002


texts: Why is magnesium hydroxide not hygroscopic?

texts:
I asked this question today and my professor was unable to provide any rationale.

I know that sodium hydroxide is hygroscopic, but why not magnesium hydroxide (at least to the same extent as $\ce{NaOH}$)? Could it be that $\ce{Mg(OH)2}$ has a higher lattice energy; the hydroxide is more closely associated with the magnesium ion and less able to react with carbon dioxide?


texts: Using knowledge of radial distribution functions, how is it possible to explain the different electron configurations of V3+ and Calcium

texts: I recognize that the 3d orbital decreases in energy to lower than the 4s once it becomes occupied (even if I don't completely understand why?!). However, how is the difference in electron configuration of Ca and V^3+ explained by the radial distribution functions? This is a question from a problem sheet at my University and I can't seem to find an answer relating to RDF's anywhere.


texts: Ionization energy of neon vs its cationic counterpart

texts:
Which requires more ionization energy: $\ce{Ne}$ or $\ce{Ne+}?$

It seems to me like it should be neon because of noble gas configuration, but the answer given is $\ce{Ne+}.$ Does this anything to do with size of the atom shrinking?

Is this because cationic counterparts always have more ionization energy than their neutral counterparts because it becomes successively more difficult to remove electrons from atoms on successive removals?


texts: Resources to learn second quantization formalism and how to implement it in code for quantum/computational chemistry research

texts:
I want to know what are some useful and practical resources to learn the formalism of second quantization as it pertains to fermions to be used in solving Quantum Chemistry problems. I am particularly asking for resources that go beyond the symbolic formalism and have guides/examples on how to implement the second quantization ideas in code (regardless of comp. language).
The pink book: Molecular Electronic-Structure Theory from Helgaker is a good start on the topic with all the formalism but I am looking for other resources with coding examples or practical implemmentations?


texts: How can the iron in the reaction of iron (ii) chloride and zinc not go to zero oxidation state?

texts:
I know that the zinc half equation would be
$\ce{Zn -> Zn^{2+} + 2e-}$.

However I am confused about the half equation for iron. I would think that since iron is completely displaced, its oxidation state goes to zero, so its half equation would be $\ce{Fe^{2+} + 2e- -> Fe}$.

However my teacher said that whenever you have iron, it will always change oxidation states from 2+ to 3+ or vice-versa in a redox reaction, and will not go to zero. For instance, she gave us an example in which there was a reaction between iron(iii) chloride and zinc. I thought that the zinc would completely displace the iron so that it goes from 3+ ion to 0 in the solid iron metal. However my teacher insisted that it goes to 2+, and not to zero.

In the example of iron(ii) chloride, I don't even see how it is possible for it to go to 3+ because then both zinc and iron are oxidised!


texts:
I am trying to add $\pu{2 g}$ of $\ce{KHCO3}$ to $\pu{20 L}$ of RO water $(\mathrm{pH} = 5.2)$ which theoretically it will add

$$
\begin{array}{lr}
\hline
\ce{K+} &\pu{10.32 ppm} \\
\ce{HCO3-} &\pu{16.1 ppm} \\
\hline
\end{array}
$$

Will my TDS measure only the $\ce{K+}~(\pu{10-11 ppm})$ or it counts also $\ce{HCO3-}~(\pu{26-27 ppm})$ (or even $\ce{CO3^2-})?$


texts: Why is the shape of sulphates and perchlorates such that lattice enthalpy doesn't decrease down the group?

texts:
The solubility of carbonates, bicarbonates and hydroxides of s-block elements increases down the group.
But, the solubility of their sulphates and perchlorates decreases down the group.
The reason for this is: down the groups, ions get larger. Thus, hydration enthalpy decreases, and solubility should take a hit. However, for hydroxides and (bi)carbonates, solubility increases. Lattice enthalpy is related to the Coulombic force between the charge centres, which decreases as the square of internuclear distance. Thus, lattice enthalpy goes down much faster than hydration enthalpy does, so on the whole, solubility does increase.
However, according to this answer, sulphates and perchlorates have a shape that ensures that lattice enthalpy decreases much slower than hydration enthalpy. Of course, this is only pushing the question one rung deeper. What is it about the shape of sulphates and perchlorates that takes care of the square factor?


texts: How to take water-dispersed PEDOT:PSS and disperse it in an organic solvent?

texts:
I am doing a science fair project on OLEDs. I am testing whether polypyrrole can be used as an emissive layer in a 2-layer OLED. The polypyrrole I am synthesizing is water soluble, and will be spin-coated onto ITO-coated glass substrate. I also need to spin-coat on a hole-injection layer (PEDOT:PSS). I can only seem to find it in what I believe to be water-dispersed form. This will cause obvious problems since both substances are water-soluble. I read on some informal message board that I could drop droplets of water-dispersed PEDOT:PSS into a hot organic solvent with a boiling point higher than water, boil off the water, and be left with organic-solvent dispersed PEDOT:PSS. That makes sense, I am just confused about what organic solvent to use. I believe it needs to have the properties of not dissolving the PEDOT:PSS, ITO, or the polypyrrole, and allow the PEDOT:PSS to become dispersed.

Here is a link to the PEDOT:PSS I am looking at:


texts: Arranging different oxygen-containing organic compounds by decreasing acidity

texts:
I am facing difficulty in the following problem.

Arrange the following compound in decreasing order of acidity.

It is clear that conjugate base of (Q) is more stable.hence it is most acidic.in R) there is much steric hinderence so my view is that it should be less acidic.however I am not sure about it.


texts: How Many mL of 1.0M HCl Would be Required to Completely Decompose Sucrose into Glucose and Fructose?

texts:
I am currently conducting an experiment into the glucose content of certain sports drinks. However, I have hit a roadblock. A majority of the drinks that I intend to test, contain sucrose. I am thinking that by adding $\pu{1.0M~ HCl}$, to say, $\pu{100mL}$ of solution (sports drink), it will decompose the sucrose into its constituents. I'm planning to use Benedict's solution and a spectroscope in order to determine the amount of glucose present in solution (I'm going to add activated charcoal to the solution to remove the coloring from it before placing in the spectroscope). As a high school student I only have limited resources.

So my question is,

Assuming there is 10 grams of sucrose per $\pu{100mL}$ of solution, what volume of $\pu{1.0M~ HCl}$ would be required to completely break apart sucrose into glucose and fructose?

Would I have to use stoichiometry to find the amount?

So far I know I have $\ce{C12H22O11 + HCl}$, What happens to the $\ce{Cl}$ from $\ce{HCl}$ when fructose and glucose is formed?


texts: Percent composition by volume of the reaction H2 + Br2  2HBr

texts:
For the reaction $\ce{H2(g) + Br2(g) <=> 2HBr(g)}$ at a certain temperature, $K=1$. Determine the composition (in per cent by volume) of the equilibrium reaction mixture if the initial mixture consisted of $3$ moles of $\ce{H2}$ and $2$ moles of $\ce{Br2}$.

The answer given is $49.6\%$ of $\ce{H2}$, $29.6\%$ $\ce{Br2}$, $20.8\%$ $\ce{HBr}$.

I made an ICE table with following data:

$$
\begin{array}{c|ccc}
   *        & \mathbf I   & \mathbf C   & \mathbf E \\
\hline
 \ce{H2}    & 3   & -x  & 3-x \\
 \ce{Br2}   & 2   & -x  & 2-x \\
 \ce{HBr}   & 0   & 2x  & 2x \\
\hline
\end{array}
$$

Using this data I made the equation:

$$
1=\frac{4x^2}{(3-x)(2-x)}
$$

My work in solving it was:

$$
(3-x)(2-x)=4x^2 \\
3x^2+5x-6=0 \\
x=\frac{-5+9.85}{6}\text{ or } x=\frac{-5-9.85}{6}
$$

I used the answer $0.808$ for $x$. I calculated the volume percents as:

$$
\%~\ce{H2} = {3-x\over 5} = 43.84\% \\
\%~\ce{Br2} = {2-x\over 5} = 23.84\% \\
\%~\ce{HBr} = {2x\over 5} = 32.33\%
$$

But, these don't match the answer given. Where have I gone wrong?


texts:
Why is p-methoxyphenol more acidic than p-methylphenol?

According to me, inductive effect really doesn’t matter at para positions and p-methoxyphenol should be less acidic due to the high mesomeric effect of the $\ce{-OCH3}$ group in comparison to the weak hyperconjugative effect of the $\ce{-CH3}$ group.

p-Methoxyphenol – $\mathrm{p}K_\mathrm{a} = 10.1$

p-Methylphenol – $\mathrm{p}K_\mathrm{a} = 10.3$


texts: Is there a standard symbol for molar density?

texts:
Is there a standard symbol for molar density, i.e. $n/V$, where $n$ is the total number of moles of every species in a system?

I realise that there is standard term "molar volume", which is the reciprocal of what I'm asking for, but my equations are going to look pretty silly with $1/V_m$ written everywhere. As a simple example, I want to say that if my system consists of a mixture of $\ce{A}$ and $\ce{B}$ with the reaction $\ce{A <-> B}$, the total concentration of $\ce{A}$ and $\ce{B}$ will be constant and we can write
$$
\ce{[B]} = c - \ce{[A]},
$$
where $c$ is the thing I'm looking for the symbol for.

I didn't find "molar density" in the IUPAC green book, but I don't know my way around it very well, and if it has a different name it might be hiding somewhere I didn't think to look.


texts: What happens to potassium if potassium permanganate is reduced in a redox reaction? How can I identify spectator ions?

texts:
I'm trying to get a fool-proof way of finding the products of a redox reaction. I can do both the oxidation and reduction the half reactions. For example in the potassium permanganate with hydrogen peroxide I found the net ionic equation to be:

$$\ce{5H2O2 + 2MnO4- +6H+ -> 2Mn^2+ + 8H2O +5O2}$$

However, this troubles me. First, what happens to the $\ce{K+}$ that was attached to the permanganate ion? My guess is that it hangs around like a spectator ion to partner up with one of the products at the end, but it can't attach to the reduced manganese because that is also positively charged.  Would it do this with the anion that was bound to the $\ce{H+}$ (e.g., $\ce{SO4^2-}$)? Would it attach to the $\ce{Mn^2+}$. Then, what does the $\ce{Mn^2+}$ cation bind to?

I get that only including the reacting species in the net ionic equation is supposed to make things easier, but it always seems to confuse me more. How do I decide what is important and what's not?


texts: Why is it easier to add bromine to styrene than cinnamic acid?

texts: Why is it easy to add bromine to styrene and why is it so difficult to add bromine to cinnamic acid? It is obvious that the $\ce{COOH}$ group of cinnamic acid affects the reaction quite a lot, but I just can't figure out why. I am guessing that the electronegativity and inductive effect of the carboxylic acid plays a key role. Any help would be greatly appreciated!


texts: Is the Arrhenius Equation a solution to a differential equation?

texts:
I just learned about the Arrhenius Equation,

$$k(T)=A\exp{\left(\frac{-E_\mathrm a}{RT}\right)}$$

and noticed that it appears to be in the same form as the solution to a linear homogeneous differential equation, so I attempted to find the associated differential equation.

Since $E_\mathrm a$ and $R$ are both constant parameters, you can treat it as a single constant. Defining $$\beta = -E_\mathrm a/R$$

we have $$\ln(k(T)) = \ln[\exp(\beta/T + \ln A)]$$

Take the derivative of each side and solve for $\mathrm dk/\mathrm dT$ ($A$ is treated as a constant of integration and goes away), and we get:

$$\frac{\mathrm dk}{\mathrm dT} = -\frac{\beta k}{T^2}$$

Here is the slope field for the differential equation when $β=-1$

and here is the slope field for $β=1$

However, since $k$ is a rate constant, I'm not sure if this method is actually applicable. Is this, or a similar differential equation actually used on this topic?


texts: LiOH hydrolysis of methyl 2,2-dimethoxyacetate not giving product?

texts:
I am forming 2,2-dimethoxyacetic acid from its methyl ester, and below is the experimental protocol I am following (from Tetrahedron 2016, 72 (3), 420–430):

  2,2-Dimethoxy Acetic Acid Formation

  Add lithium hydroxide monohydrate ($\pu{89.5 mmol}$, $\pu{3.75 g}$, $\pu{1.2 equiv}$) to a solution of methyl dimethoxyacetate ($\pu{74.6 mmol}$, $\pu{10 g}$, $\pu{1 equiv}$) in dioxane ($\pu{45 mL}$) and water ($\pu{45 mL}$) at $\pu{0 ^{\circ}C}$.
  Stir the mixture for $\pu{1 h}$ at $\pu{0 ^{\circ}C}$ and one additional hour at room temperature.
  Add sodium hydroxide ($\pu{1M}$ aq soln, $\pu{75 mL}$) to the mixture.
  Extract the mixture with diethyl ether ($\pu{375 mL}$).
  Acidify the recovered aqueous layer with hydrogen chloride ($\pu{6N}$ aq soln) until a pH of 1-2.
  Extract the organics with diethyl ether ($\pu{375 mL}$).
  Dry the combined organic layers with magnesium sulfate and filter.
  Evaporate the solvent slowly under reduced pressure to obtain 2,2-dimethoxyacetic acid.

I repeated this reaction many times but every time I check the $\mathrm{^{13}C}$-NMR, I only see a single peak at $\delta \: \pu{67.12 ppm}$. I believe this corresponds to C-OMe. By theory (and by literature) I should see 3 peaks.
$\mathrm{^{1}H}$-NMR does show 6:1 ratio of singlets at $\delta \: \pu{3.704 ppm}$ (6H) and $\delta \: \pu{3.458 ppm}$ (1H) but it is not well aligned with literature; By theory, a single hydrogen atom adjacent to $\ce{C=O}$ group should be more deshielded than $\delta \: \pu{3.458 ppm}$ (i.e. be placed at higher ppm). I thought through what I have done and I still can't figure out which step has gone wrong. Any thoughts and ideas? Would appreciate any advice.


texts: Simplest way to balance any chemical equation

texts:
In your opinion, what would be the simplest way to balance any size of the chemical equation?

For example here is an equation:  $$\ce{C12H26 + O2 -> CO2 + H2O}$$

I saw some ways by putting letters in front of each molecule, but I just don't get too much how to do this with this method! My teacher is always speaking about another method, but it simply doesn't feel logic/mathematics is enough for me.


texts: Virial equation of state - Taylor expansion

texts:
I don't get how Taylor expansion over $ \frac{1}{\overline{V}} $ of Virial equation of state is caried out: $Z = \frac{P\overline{V}}{RT} $ which yields
$$ Z = 1 + \frac{B_{2V}(T)}{\overline{V}} + \frac{B_{3V}(T)}{\overline{V^2}} + ...
$$ I thought I understood calc2 Taylor expansion of form $$f(x) = \sum\limits_{k=0}^\infty \frac{f^{(k)}(0)}{k!} x^k $$ so maybe I was in illusion. What's is $Z$ function of? At what expansion point do we expa


texts: Amber solvatebox: How do I remove water that has traveled away

texts:
I used Amber's solvatebox function with a small polypeptide and tip3p water with a distance of 15 angstroms between the molecule and the edge of the box.

After I ran dynamics, I tried to view the output by removing water from view in Jmol, but I had a really hard time rotating the polypeptide. When I viewed it with water, I found that the difficulty in rotating was because the radius of rotation (are those the right words?) was extremely large because some waters floated off in the distance.

I want to remove these stray waters. How would I go about doing that? Would I just crack open the output and remove those waters by deleting lines that contain information for those particular waters?


texts:
I was wondering if anyone knows where I can find UV-VIS spectra of the n-decanes.  Specifically tetradecane and dodecane.  I can't seem to find such information using my regular search methods, so I was wondering if there was a common database that contains such things that I am simply unaware of (likely).

All I really need to know is if these chemicals will absorb radiation with wavelengths between 355-375 nm.  A source to back this up will only help.

Thanks,
Sam


texts: I've read that for an oxyacid, the oxidation number of the central atom shows the power of that acid, but here, the oxidation numbers of sulphur in sulphuric acid and pyrosulphuric acid are both the same, i.e. +6. That is confusing! How should I proceed now?


texts: Is there a silicon equivalent to a carboxylic acid?

texts: Can terminal Si on a siloxane chain have double bond O and OH?


texts:
comfrey (Symphytum officinale) is a well known plant to organic growers. One of its features is that the leaves break down very quickly, either in water or in a container closed from UV light. There must be some chemical explanation for this, can you explain to me what that is ?

Thanks Erin


texts:
What is the best way of preparing an aqueous solution containing 5 mM
$\ce{CdSO4}$, 1 mM $\ce{SeO2}$, 0.5 M $\ce{Na2SO4}$ and adjusting pH to 3 by adding 0.5 M $\ce{H2SO4}$?

What is the conventional way of doing it (in industrial chemistry or simply just the labs)?


texts: Using cryptands to make a negatively-charged solution?

texts:
In our discussion group, my friend mentioned that metal cations can be separated from other cations in solution using cryptands. After addition of the cryptands to the solution of the cations, chelation of the cations takes place and since the complexes formed are more soluble in organic solvent, addition of an organic solvent to this resultant solution would allow these complexes to be migrate to the organic layer. The organic layer can then be decanted and the metal ions have now been separated successfully from the aqueous solution. This was my friend's proposal.

From hearing this, I quickly thought of the possibility of creating a negatively-charged solution. By applying the method of using cryptands which my friend has proposed to separating sodium ions from a solution of sodium chloride, wouldn't the remaining chloride ions in solution give the resultant solution an overall negative charge? This led me to think that there must be something wrong with his idea as this should not be able to occur, based on my instinct. However, I do not know exactly how to refute my friend, to say his proposal does not work. Thus, I would like to ask if anyone knows the reason why my friend's method would not work.


texts:
Let's take an acid, $\ce{HCl}$;

Now what do you mean by the $p\ce{H}$ of $\ce{HCl}$? Does $\ce{HCl}$
 have free floating ions in it like water does?

Also, why can't the $p\ce{H}$ value of a substance be less than $0$? Like can't a substance have $10^1~\rm M$ of $\ce{H+}$ ions? In that case won't the $p\ce{H}$ be $-1$?

And when we talk about $p\ce{H}$ values, then are we talking about Arrhenius acids and bases or Brønsted–Lowry  acids and bases?


texts: Condition For NaHCO3 to react to form CO2 with organic acids

texts:
My professor told us the following:

  $\ce{NaHCO3}$ will react to evolve
  $\ce{CO2}$ whenever the acidic nature of the reactant exceeds the
  acidic nature of benzoic acid.

I want to know why this is. And is the given statement valid? He didn't give us the reason.  And in that case should $\ce{NaHCO3}$ react with 1,2-dihydroxy
cyclobutanedione to evolve carbon dioxide?


texts: Does cooling a potato change the nature of its carbohydrates?

texts:
A talk-show guest of Joe Rogan claimed that cooling a potato after cooking creates "resistant starch" that's better for human consumption

https://www.youtube.com/watch?v=niwqfwA2Lb8

The claim is also made here: https://www.healthline.com/nutrition/cooling-resistant-starch

This seems to contradict everything I know about chemistry, since cooling only slows down all chemical processes.

Is there any validity to the claim? What is this "resistant starch"? Why does cooling the potato after cooking create it?


texts: Why n-alkanes can be found in organic solvent extract of rubber?

texts:
Sorry for the confusing title, I didn't know how to describe this better. So, if we douse rubber, say, a bicycle tire or a certain type of rubber glove, with organic solvent (n-heptane), we can find n-alkanes being dissolved in the solvent. Why is this? I'm talking especially about gas chromatography to analyse the paraffinic hydrocarbons here.

I guess this is quite a trivial question but I can't figure it out. As far as I know, natural rubber consists mainly of isoprene polymer chains. But isoprene has a double bond and in GC chromatogram we can see n-alkanes being the largest peaks. And not only that, we can also find straight chain hydrocarbons in synthetic rubber (like NBR or SBR) solvent extracts. SBR has a benzene ring in its structure but still n-alkanes are the dominant finding in its solvent extract chromatogram.

This is a major subject in my bachelor's thesis but I'm an analytical chemistry major and struggling a bit with materials science in this depth. Any advice and ideas would be greatly appreciated.

To make my point clearer I present these two chromatograms:

(GC-FID run of pure n-heptane)

(GC-FID run of n-heptane extract of bicycle tire)

This question still haunts me. I found this. Could that be a partial explanation for the aliphatic hydrocarbon finding?


texts:
I know buffer capacity is the following:
$$β=\frac{Δ(\ce{H+})}{Δ(\mathrm{pH})}$$ specifically the amount of acid/base that needs to be added to change pH by 1 unit.

If I have data about how pH of a protein has changed upon adding specific amounts of acid, how do I calculate buffer capacity?
Is there any reason why the change in pH needs to be 1? If I calculate how much acid needs to be added for the pH to change by 1.1, can this be scaled to determine amount of acid needed to change pH by 1?


texts: Why must both the critical temperature and pressure be exceeded to achieve the supercritical phase?

texts:
The characteristics and properties of supercritical fluids and the associated vapor-liquid critical point are well established.  One thing that I've always been curious about, though: what is the physical explanation for why it's necessary for both the critical temperature and critical pressure both to be exceeded simultaneously in order for this phase transformation to occur?

ChemWiki's description ("Critical Point") provides some measure of an explanation:

  [A]bove the critical temperature, it is impossible to condense a gas into a liquid just by increasing the pressure. All you get is a highly compressed gas. The particles have too much energy for the intermolecular attractions to hold them together as a liquid. The critical temperature obviously varies from substance to substance and depends on the strength of the attractions between the particles. The stronger the intermolecular attractions, the higher the critical temperature.

Is there more to the physics than just "[t]he particles have too much energy for the intermolecular attractions to hold them together as a liquid"?

Per an early comment by Mithoron, the fact that increasing pressure on a supercritical fluid can eventually drive it to a solid phase would seem to imply that it's not quite that simple.  See, for example, the phase diagram of carbon dioxide(source):


texts: Why can't an "upside down" chiral molecule neutralize the polarized light effect?

texts:
Steve Mould did a nice video a few months back called "Why Sugar Always Twists Light To The Right" (link is timestamped at the critical part).

However his explanation was not complete.
He explains that molecules that have mirror symmetry, ultimately cancel each other out because any polarized light that gets warped by one molecule, gets de-warped by the next "mirrored" molecule.
However, he continues, chiral molecules (which are like hands, in that left and right cannot be "stacked"), don't do this because they don't have mirrored molecules, so any effect on polarized light passing through never gets "undone". It only gets "twisted" in one direction.
Here's what remains unexplained:
Even two left hands CAN be stacked in such a way that they WILL cancel each other out. Yes perhaps they will not be oriented in a "high five pose", but in a floating stew why can't they be lying on top of eachother in such a way that they completely cover eachother and undo eachother's effect?


texts:
I'm studying Wolff-Kishner reduction and I don't understand why after this step

the leaving group is $\ce{OH-}$ instead of $\ce{^-HN-NH2}$. I guess it's because hydroxide ion is less strong than the other although it would be useful to know if i can calculate pkb of diazanide (namely $\ce{^-NH-NH2}$) starting from data on hydrazine. Also I'm considering pkb of $\ce{OH-}$ equal to $0$ because it's acting as a base.


texts: How are there three possible tautomers of 2,2,4-trimethylheptane-3,5-dione?

texts:
The answer for the above question is three. But I am able to draw four structures:

Where am I getting it wrong?


texts: Name for analog of salt hydrate with non-water solvents?

texts: Salts can bind with some water to form hydrates. For example, we can call $\ce{CoCl_2\cdot 6H_2O}$ cobalt chloride hexahydrate. There is no reason that water should be the only solvent that can bind with salts though. Dimethyl sufloxide is pretty polar and can dissolve some salts, so I might hypothesize that we could make salt crystal that has some bound into it, say $\ce{CoCl_2\cdot 6DMSO}$. I might call that cobalt chloride hexadimethyl sulfoxate, but that is totally made up. Is there a name for that sort of thing?


texts: How would you go about adding a Cl group para to a brominated cinnamic acid?

texts: We recently synthesized brominated cinnamic acid in lab, and now our goal is to add a Cl para to the R group attached to the benzene ring.


texts: What determines the atom or molecule that receives electrons during oxidation?

texts:
I'm no chemist, so bear with me.

From my understanding, the reason metal oxidation occurs is because the metal is losing electrons to the oxygen ions in the air; and that an ion is an atom or molecule which either has more or less electrons than the "standard" of that atom/molecule; which is why it's "taking" electrons from something else.

What prompts my question has to do with soldering. I'm learning that one reason for the use of flux is to prevent this oxidation and protect the soldering tip. So according to what I said before, a soldering iron becomes oxidized because it has lost electrons to the air, and the high temperatures hasten this process.

Now to get to the detailed question: I understand the very basic oxidation process. But, once the metal has lost electrons, doesn't that now make it composed of ions? If so, Why does the metal continue to corrode? Why isn't the metal now taking electrons and virtually "restoring" itself? What is it about oxygen ions that make them the ones that take electrons from metals such as copper? Why isn't copper the one taking electrons from the air? Does it have to do with valence electrons or electron shells or something?


texts: Which Phenols give the colours blue, green or violet in the neutral FeCl3 test?

texts: I have read about the neutral FeCl3 test for Phenols, where a positive test is indicated by the colour of the solution which ranges from green to blue to violet. But which specific derivatives of phenol give a specific colour? Or is it random?


texts: How does a photochemical reaction of lignin with oxygen (yellowing of paper) produce chromophores?

texts:
Edit:  This question is about chromophore production in lignin as found in low cost or short-term use paper such as newsprint. A different, excellent answer describes oxidation yellowing of the cellulose found in books.

This answer contains a quote from "Stuff Matters" by Mark Miodownik:

  Lignin reacts with oxygen in the presence of light to create chromophores ( meaning, literally, 'color carriers'), which turn the paper yellow as they increase in concentration. This type of paper is used for cheap and disposable paper products, and is why newspapers yellow quickly in light.

I've read here that bleach and peroxide can oxidize chromophores by reacting with double bonds, reducing or removing the appearance of color. In this particular case of what sounds like a photochemical reaction of lignin with oxygen, how is a chromophore produced?

Or, is it really even true that a chromophore is responsible for the yellow color of yellowed paper? Or is it the oxidation and loss of a fluorophore that was originally making the paper look white? I'm not sure of that, because the phenomenon seems to be pretty old, possibly before the use of fluorophores in paper manufacture.


texts: Estimation of dipole moments in aromatic compounds

texts:
If it asks to compare dipole moment in aromatic compounds then do we see inductive or resonance effects or do we see a mix of both?
E.g. we have to compare dipole moment in pyrrole and furan then in one we have opp direction of dipole moment in both why? Like it's a specific question but I wish to understand the mechanism behind every such tricky question so that I can do on my own.
Or suppose we have ortho hydroxyphenol then what would I say the direction of dipole moment would be? Would it be inwards towards benzene or outwards towards $-\ce{OH}$ group. It's not because of convention doubt, but like whether it's the resonance effect that dominates which would result in majorly + on $-\ce{OH}$ group and - on $-\ce{Ph}$ group or is it the inductive effect dominating which would result in opposite sign.


texts:
I stumbled upon an exercise asking to draw the resonance structure of $\ce{SO4^{2-}}$.

We can choose between the resonance structures by calculating the formal charges and by checking which one gives out the least value, and which one has the negative charges on the more electronegative atom.

My Chemistry Textbook "Chemistry 10th edition" by Chang states that:

  The general rule for elements in the third period and beyond is that a resonance structure that obeys the octet rule is preferred over one that involves an expanded octet but bears fewer formal charges.

As I've searched more about this example , I've found out that most exercises that treated this molecule have labeled the one that has the least formal charge as the more stable.

This got me confused, is the resonance structure which obeys the octet rule the more plausible or is it the one which has the least formal charge?


texts: Should we expect Jahn–Teller distortion in bis(ethylenediamine)nickel(II)?

texts:
(ii) The stepwise stability constants of the following complexes in aqueous solution at $\pu{25 °C}$ are given below:
$$
\begin{array}{cll}
\hline
\ce{M} & \ce{[M(en)2(H2O)2]^2+} & \ce{[M(en)3]^2+} \\
\hline
\ce{Cu} & \pu{1E9} & 0.1~\text{(estimated)} \\
\ce{Ni} & \pu{1E6} & \pu{1E4} \\
\hline
\end{array}
$$

I got this data from an assignment problem. In the case of copper it makes complete sense for the stability constant of formation of $\ce{[Cu(en)_3]^{2+}}$ to be that low given that we have $\mathrm{d^9}$ configuration and strong Jahn–Teller (JT) distortion leading to strain in the rings formed in the complex.
But I can't figure out if there'll be any distortion in the $\ce{[Ni(en)_3]}$ ($\mathrm{d^8}$ configuration). Initially, I assumed there'll be no distortion and the complex would be satisfied with the chelation alone (compromising on the stability provided by JT distortion). But then some of my friends pointed out that $K$ reduces from $10^6$ to $10^4$ so there must be some kind of distortion. After some googling, the only article with some data I could find is by Sohail et al. [1].
In the linked article, there are no comments on JT distortion. Instead, packing effects have been held responsible for the natural distortion of the complex (the last line under Comment section). But I am not entirely convinced; so my questions are:

Would the $\mathrm{e_g}$ orbitals be symmetrically or asymmetrically filled?

If asymmetrically, then why is the JT distortion so profound in the copper(II) complex but weaker in the nickel(II) complex? And if it's symmetrically filled, then what is responsible for the decrease in the stepwise stability constant?

References

Sohail, M.; Molloy, K. C.; Mazhar, M.; Kociok-Köhn, G.; Khosa, M. K. Tris(ethylenediamine)nickel(II) tetraiodocadmate(II). Acta Cryst E Struct Rep Online 2006, 62 (2), m394–m396. https://doi.org/10/b82dng. (Open Access)


texts:
How is the redox couple as it is written for the oxidation of $\ce{MnO4-}$, as $\ce{MnO4-,H+/Mn2+,H2O}$ correct?

I agree that $\ce{MnO4}$ is being oxidized as it loses electrons (going from -1 charge to +2) but I don't see why $\ce{H+}$ is also being oxidized. Could someone explain?


texts:
According to the Arrhenius definition of acids:
An Arrhenius acid is any species that increases the concentration of
hydrogen ions in its aqueous solution.
Hydrogen Chloride gas ionises in water to give hydrogen and chlorine ions. Thus, it increases the concentration of hydrogen ions in the solution. So is hydrogen chloride gas considered to be an Arrhenius acid or is the aqueous solution of hydrogen chloride, i.e., HCl(aq.) gas an Arrhenius acid?
If the aqueous solution is an acid then why is hydrogen chloride gas referred to as an ‘acidic’ gas?
Similarly, is NaOH(s) an Arrhenius base or is NaOH(aq.) an Arrhenius base?


texts: What does pO2 of blood mean and why do we use it?

texts:
I understand the basic Dalton's law of partial pressures in gases. Also, Henry's law of diffusion, says, the concentration of gas dissolved in a fluid is proportional to the partial pressure above it.

So if we say that the $p(\ce{O2})$ of oxygenated blood is $\pu{100 mmHg}$, where is the free gas existing in equilibrium with dissolved gas? Does it mean that the blood has a concentration of oxygen equal to that when placed in a surrounding of $p(\ce{O2}) = \pu{100 mmHg}$? If yes, why don't we directly report in concentrations instead? Is it easier to measure?

Wikipedia also says that the Henry's law doesn't stand if the gas is reacting. But isn't oxygen reacting with the Haemoglobin?


texts: How do I eliminate the disagreeable odor of soy milk?

texts:
I've was making tofu from soy-milk, but noticed this disagreeable odor produced during the process.

I conducted a string of internet searches in an attempt to find a method to eliminate this odor.

I learnt that the enzyme lipoxygenase is primarily responsible for this odor, and is activated upon grinding soy beans in water. Additionally, it appears that lipoxygenase is inactivated in the presence of  D-glucose and the enzyme glucose oxidase.

Obtaining D-glucose is fairly simple, but I'm at odds as to where I can find glucose oxidase.

Further investigation suggests that commonly available honey contains glucose oxidase.

Armed with this knowledge, I want to know:

Can I add a measured quantity of dilute honey, along with some D-glucose, to the soy milk and inactivate the lipoxygenase enzyme this way?

One more query...
I found somewhere that glucose and glucose oxidase in water, makes hydrogen peroxide and this H2O2 inhibit the lipoxygenase enzyme... So my query is.... What, if add hydrogen peroxide directly, in a measured quantity, in water and grind the soybeans with this solution.


texts: What is the the full name of TAPD? Structure provided

texts: I have a substituent called TAPD on a molecule I'm working with. I have a hard time locating information about its properties. The bold square in the picture below is supposed to be the rest of the system on which the TAPD is attached. I am a physicist and thus not very good at chemical naming, so I would have good use of some help.


texts: What is the modern hardware/supermarket term for 'laundry bluing'?

texts:
I want to make this amazing paper Crystal Tree with my kids. One of the ingredients is laundry bluing. It is described thus:

  The magic crystals that are left behind are a combination of the Mrs. Stewart’s Bluing and the table salt. The solution that you created is supersaturated by the bluing and salt that you add to the water. The bluing is a colloid, with many tiny particles suspending themselves within the water. It’s just like when you shake up a snow globe, except the particles of bluing are much smaller than the snow. As the bluing and salt water make their way up the tree, the water begins evaporating. These means there is less water able to support the bluing particles and dissolved salt. This evaporation allows the salt and bluing particles to crystallize, resulting in your beautiful tree.

No one in my supermarket has heard of laundry bluing. Is it possible it is hazardous and has been banned in some states/countries? Perhaps it has another name? Perhaps this has a chemical name?

My question is: What is the modern hardware store/supermarket term for 'laundry bluing'?


texts: Is it possible to calculate chromacity coordinates using absorbance values?

texts:
I have absorbance values for blood plasma. Absorbance was measured in range of 380 – 600 nm every 5 nm ending up with absorbance values for 45 wave lengths.
I was browsing through literature, and  I came  across chromacity coordinates (XYZ) and this seems to be a very convenient way of summarizing data about color in just two data points.
I have been reading some literature about different colorimetric systems, but since my background is in genetics, it didn’t make much sense for me.
Therefore, I would like to ask you if it is possible to calculate these chromacity coordinates using my absorbance values and if so does anyone now some kind of software for this or exact formulas on how to do it?


texts: What is the effect of adding salt to ice?

texts: What will happen to the melting point temperature of ice if some common salt is added to it? How to justfy the answer?