texts: Calculate chemical potentials to find electrode Fermi level

texts:
I'm running some simple simulations of the semiconductor-electrolyte interface and I'm having a hard time figuring out the equilibrium condition. Can someone please help me with my electrochemical potentials equation? Here's my thought flow so far:

I'm interested in finding out what is the Fermi level in the SC at equilibrium for OER: $4OH^- = O_2 + 2H_2O + 4e^-$. So I start by writing the condition for equilibrium:

$4\tilde \mu_{OH^-} = \tilde \mu_{O_2} + 4 \tilde \mu_{e^-} + 2 \tilde \mu_{H_2O}$

Since $O_2$ and $H_2O$ have no charge, their electrochemical potential is just their chemical potential ($\tilde \mu_{O_2} = \mu_{O_2}$ and $\tilde \mu_{H_2O} = \mu_{H_2O}$).

Moreover, the $\tilde \mu_{e^-}$ electrochemical potential of $e^-$ in my semiconductor electrode is just the Fermi level $E_F$ I'm looking for. Keeping in mind that $\tilde \mu_i = \mu_i^0 + RTln(a_i)  + z_iF\phi$ and that the activity of water $a_{H_2O}=1$, I arranged the balance equation to:

$E_F = (\mu^0_{OH^-} - \frac{1}{4}\mu^0_{O_2} - \frac{1}{2}\mu^0_{H_2O}) + RTln\left(\frac{a_{OH^-}}{\left( \frac{p_{O_2}}{p^0}\right)}\right) -F\phi_{sol}$.

I can calculate the electrical potential $\phi_{sol}$ at the interface in the solution with the Poisson equation. I can calculate the activity coefficient $a_{OH^-}$ based on the $[OH^-]$ concentration at the interface and of course I know the partial pressure of $O_2$. My problem is how do I determine the chemical potentials at standard conditions from the first parantheses?

$(\mu^0_{OH^-} - \frac{1}{4}\mu^0_{O_2} - \frac{1}{2}\mu^0_{H_2O}) = ???$

Could I related them somehow to the SHE electrode which I know to be approx $4.5\ eV$ vs. vacuum?


texts: How to derive the steady-state solution for simple two-step reaction with differential equations?

texts:
Consider this simple two step reaction, a variant of a Michaelis-Menten type of problem, where $\ce{A}$ and $\ce{B}$ reversibly bind to make $\ce{AB}$, and $\ce{AB}$ and $\ce{C}$ reversibly bind to make $\ce{ABC}$:

\begin{align}
\ce{A + B  &<=> AB}\\
\ce{AB + C &<=> ABC}
\end{align}

Assume all the rate constants are equal to $k$ for simplicity, and that $[\ce{A}]_0$, $[\ce{B}]_0$, $[\ce{C}]_0$ are initial values for $\ce{A}$, $\ce{B}$, $\ce{C}$, and $[\ce{AB}]_0 = [\ce{ABC}]_0 = 0$.

What is the proper way to derive the steady-state concentration of $\ce{ABC}$ as a function of initial values? here is an attempt to get $\mathrm{d}[\ce{AB}]/\mathrm{d}t$:
$$\frac{\mathrm{d}[\ce{AB}]}{\mathrm{d}t} = ([\ce{A}][\ce{B}]k + [\ce{ABC}]k) - ([\ce{AB}]k + [\ce{AB}][\ce{C}]k)$$

The first parenthesis of the sum are the two ways to make $\ce{AB}$ and second parenthesis are the two ways to lose $\ce{AB}$.
We can set $\mathrm{d}[\ce{AB}]/\mathrm{d}t = 0$ and try to solve for $[\ce{ABC}]$, but I am not sure how this helps and where initial values come in.


texts: Pressure exerted by the mixture of nonreactive gases

texts:
$\pu{2.0 L}$ of $\ce{O2 (g)}$ and $\pu{8.0 L}$ of $\ce{N2}$, each at $\pu{0.00^\circ C}$ and $\pu{1.00 atm}$, are mixed together. The nonreactive gaseous mixture is compressed to occupy $\pu{2.0 L}$ at $\pu{298 K}$. What is the pressure exerted by this mixture?

I tried to solve this problem by first using

$$P_\mathrm{tot}=\frac{n_\mathrm{tot}RT}{V}\quad(T=\text{constant}; V=\text{constant})$$

then using

$$V_\mathrm{tot}=\frac{n_\mathrm{tot}RT}{P}\quad(T=\text{constant}; P=\text{constant})$$

Plugging in the numbers for the second equation

$$10=\frac{n_\mathrm{tot}\cdot 8.314\cdot 273}{101325}$$
$$n_\mathrm{tot}=\pu{0.45 mol}$$

Then plugging in the numbers for the first equation

$$P_\mathrm{tot}=\frac{0.45\cdot 8.314\cdot 298}{2}=\pu{6.76 atm}$$

Whereas the answer is $\pu{5.5 atm}$. What am I doing wrong here?


texts:
The Wikipedia article on metals describes them as elements whose polyatomic configurations* exhibit any one of a number of patterns. I could not discern any property that characterized all the patterns.

To the best of my knowledge, there are two main categories of elements: metals, non-metals. There's a third category, metalloids, whose members are those that satisfy some of the criteria for inclusion in both main categories.

It would seem very odd if there were nothing that characterized all, and only, metals. In fact it would seem that metals are better conceived of as an arbitrary grouping of what is actually a number of other categories, each of which would include all, and only, the elements that exhibit a single type of polyatomic configuration*.

Is there a characteristic that characterizes all, and only, metals?

*(I'm using the phrase 'polyatomic configuration' in order to express 'the way that atoms of a particular element stick together when you have a number of atoms of that element connected together'. Is there a standard term that expresses that idea?)


texts: On the use of hexane in the organic reduction by DIBAL-H

texts:
In some variations of the organic reduction by DIBAL-H, I've seen hexane used, as in this equation from this website;

I've looked it up, but I haven't seen any explanation for why hexane's used there. It's also seen in the action of DIBAL-H on alkyl nitriles to give aldehydes with ammonia.
Can anyone help me with why it's used in both cases?


texts: What is the exact statement of Drago's rule?

texts:
While studying the topic of chemical bonding, I came across a statement given by my teacher:
Elements of the third period and above do not show hybridisation. An example, in the case of $\ce{PH_3}$, $99.9$% s-character exists in the lone pair due to $\ce{P-H}$ bonds being weaker.
Is this the exact statement of Drago's rule? On various other sources, I have found conflicting views, some say that hybridization actually exists and the actual statement is different, the one being taught to students is wrong.
What is Drago's rule? Does it really exist?
I had gone through this answer, it basically explains a quantum mechanical reason for explaining the observation. What I'm seeking is the exact statement of Drago's rule.
For example, in $\ce{PH3}$ does the lone pair exist in pure s-orbital or in a hybrid orbital that is not $\mathrm{sp^3}$ but some other orbital whose nature can be explained and generalized by Drago's rule?


texts: Do we need to check for all kinds of symmetry in a compound to declare it achiral?

texts:
I know that a compound is achiral if it contains any one of the following kind of symmetry.
1.Plane of symmetry
2.Centre of symmetry
3.Normal axis of symmetry
4.Alternate axis of symmetry
It is difficult to write, for many compounds, its mirror image and then check using visualisation that if the image and compound are same or not, so we check for these 4 symmetries in molecule. My question is that for any compound do we need to check for all the symmetry elements one by one till we get a symmetry possessed by the molecule to declare it achiral, for example, does there exist any compound which has only alternate axis of symmetry and not any other kind of symmetry, so that any one will have to check all the symmetries one by one, till he reaches alternate axis of symmetry, to declare it achiral?
I know compound which have centre of symmetry, but not plane of symmetry, but  I don't know about a compound which has only alternate axis of symmetry and not any other kind of symmetry. Most of the achiral compounds that I have come across have plane of symmetry or centre of symmetry. So, do we need to check for all axis of symmetry or only centre and plane of symmetry, or any other shorter combination?


texts: Why does the d orbital size decreases on addition of electrons?

texts:
In Concise Inorganic Chemistry by JD Lee (4th edition; adapted by Sudarshan Guha), on page 80 under section 3.7 "The Extent of d-orbital Participation in Molecular Bonding" it is given:

  A second factor affecting the size of d orbitals is the number of d orbitals occupied by electrons. If only one 3d orbital is occupied on an S atom, the average radial distance is $2.46$Å, but when two 3d orbitals are occupied the distance drops to $1.60$Å.

I wish to know the reason why the size of the d orbital drops when additional electrons are added. I think this is counter-intuitive since on addition of an extra electron the interelectronic repulsions increases and confining them to a small volume increases overall energy of the system thereby making it unstable. So, I think the orbital size must increase, but it is happening the opposite way.

Kindly explain the above-mentioned concept.


texts: Do we neglect the temperature changes during a reaction while calculating delta(H)?

texts:
Suppose for a reaction: $$\ce{$a$A + $b$B -> $c$C + $d$D }$$

we know the $\Delta U$ as $\mathrm dU$ and all the components of the reaction are gas.

Then to calculate the $\Delta H$ at a temperature $T$ we use the expression $\mathrm dH=\mathrm dU+\left(c+d-a-b\right)RT$.

Then while using this expression did we assume the temperature to remain constant as it wouldn't really be constant as the actual expression for $\mathrm dH$ is: $\mathrm dH=\mathrm dU+\left(pV\right)$ and so we can write $\mathrm dH=\mathrm dU+\mathrm d(nRT)$ and for $\mathrm dH=\mathrm dU+\left(c+d-a-b\right)RT$, $T$ has to be constant?


texts: How to figure out the state of aggregation of an unknown substance via properties of a chemical equilibrium in a closed system?

texts:
This is a question from the College Entrance Test in China.

In a closed, constant temperature container, reaction $\ce{A(s)<=>B +C(g)}$ reached chemical equilibrium. If the volume of the container is reduced, when the equilibrium is reached again, the concentration of $\ce{C}$ equals the concentration of $\ce{C}$ before the reduction.
Is it possible that $\ce{B}$ is in gas state?

The official answer is impossible.
And the official explanation to this is:

If $\ce{B}$ is in gas state, we have $K=C_\ce{B} \cdot C_\ce{C}$
Otherwise, if $\ce{B}$ is in liquid or solid state, we have $K=C_\ce{C}$
Since the concentration of $\ce{C}$ does not change after the reduction, in order to remain the $K$ value unchanged, $C_\ce{B}$ must not be involved in this process. So $\ce{B}$ is impossible to be in gas state.

But I don't think it makes sense.
Consider a container with a volume of $V$, $b$ mol of $\ce{B(g)}$ and $c$ mol of $\ce{C(g)}$ is inside it.
If   $K_{\text{pre}}=K_{\text{post}}$
, we have $C_{\ce{B},\text{pre}} \cdot C_{\ce{C},\text{pre}}=C_{\ce{B},\text{post}} \cdot C_{\ce{C},\text{post}}$.
When the container's volume is reduced by $\frac{1}{2}$, if $\dfrac{b_{\text{post}}}{b_{\text{pre}}}=\dfrac{c_{\text{post}}}{c_{\text{pre}}}=\dfrac{1}{2}$, the equilibrium can be reached, with all the requirements stated in the question.
Conclusion: $\ce{B}$ can be in gas state.
So, is the official answer wrong or I just didn't make the right conclusion?


texts: Mercury vapor release from amalgam fillings

texts: What would cause vapour release from elemental mercury? Would it be pressure, friction... could one stop the vapour release through cooling the mercury?


texts: How is red oxide of copper converted into black oxide & vice versa?

texts:
I can't really find any information about it.
Any help would be appreciated.


texts: How to determine mobility when two mechanisms exist simultaneously

texts:
Two scattering mechanisms exist in a semiconductor. If only the first
  mechanism is present, the mobility will be $\pu{250 cm2/V s}$. If only the
  second mechanism is present, the mobility will be $\pu{500 cm2/V s}$.
  Determine the mobility when both scattering mechanisms exist at the
  same time.

I'm not sure what the last sentence is trying to tell me. I know mobility is $q\tau_c/m_n$, and I think I need to solve for mean free time here to help, but I'm not sure what I should use for $m_n$ since I don't know what the semiconductor is, and I'm not given a value.

Although, since I'm given two mobilities to start with, should I solve for $\tau_c$ twice and average those? Really not sure what direction I should be going in (if only my professor answered his emails).


texts: Why do heavier elements have smaller specific heat values.

texts: In the periodic table the trend is that as the mass of each element increase's the specific heat tends to go down. This seems to be counter-intuitive because if I am not mistaken as mass increase's the amount of heat that the substance can hold goes up. So why does the specific heat of these elements go down?


texts: How to calculate number of each type of atom in a residue in PyMOL?

texts:
I have a 3D model of PDB 4UDC (dexamethasone bound to human glucocorticoid receptor), and I'd like to calculate how many atoms of each element are in the dexamethasone molecule (which has the residue name DEX) in this model, just to make sure it is correct (as I have added hydrogen atoms with h_add and if I missed a double bond it will be off). So how do I determine how many atoms of each element are present in this residue?

The sort of output I'd be looking for, from whatever answer you provide, would be something like:

C22H29FO5

if I got the bond order and everything else right. Just so you know, as I would dislike it if you thought I meant if we were to count all the atoms up altogether (which would be $22+29+1+5=57$).


texts: Does a weak buffer solution still maintain a mostly steady pH if the acid or base load it has to buffer is small?

texts:
I need to buffer the $\mathrm{pH}$ of a solution to $3.0$ using a citrate buffer.  I found a recipe to make a buffer solution that would use $82\%$ of $0.1\,\mathrm M$ citric acid (monohydrate) and $18\%$ $0.1\,\mathrm M$ trisodium citrate dihydrate to give a citrate buffer with a $\mathrm{pH}$ of $3.0$.  The purpose of buffering the $\mathrm{pH}$ to $3$ is that this solution contains an active ingredient that has a very short shelf-life at a more neutral $\mathrm{pH}$. The buffer solution will make up about two-thirds of the solution by weight, and isopropyl alcohol will make up about $30\%$ of the solution.  Assume all of the remaining ingredients are non-dissociable in the relevant $\mathrm{pH}$ range, except for the active ingredient which has the following properties:

Concentration of $0.03\%$ by weight
A single weakly basic moiety with a $\mathrm pK_\mathrm a$ of $11.45$
Molecular mass of approximately $420\,\mathrm{g\over mol}$

Since this will be applied to skin, I'd like to use the weakest buffer solution that would still maintain the $\mathrm{pH}$ at $3.0$.  My question is, if I use $0.01\,\mathrm M$ or $0.001\,\mathrm M$ solutions to make the buffer, would it still be able to buffer the $\mathrm{pH}$ at $3.0$?


texts: How can I make an acidic pen to burn paper on writing on it?

texts:
If I have a pen with refillable ink, can I just pour in concentrated Hydrochloric acid or concentrated sulfuric acid in the ink chamber to make it an acidic pen?

Would it be better to use the acid of suitable molarity instead of being concentrated?

Then if I write with it on a paper, will it burn?

Is this a good idea to play with?

Is it dangerous in any way?

Is it illegal to make such things for experimenting and fun?

Is there any other safe method to achieve the same?

What are the odds that the poured acid will burn the ink chamber itself and start leaking?

Can it be used in any constructive way? Like cutting many sheets of paper at once. Or using it in industries suitably to make smooth cuts in materials that can be burned with the used acid.

Will it be fun to you?

Thanks to everyone.

Edit:

I would like to add a few details.

Assume that the acid is not concentrated but of suitable molarity to just cut the paper. I mean, to pierce through it and burning its edges to just make a nice cut. Like a glowing incense stick makes when made to touch a paper.
Also, the nip of the pen and the ink chamber are strongly inert; enough to survive the concentrated acid's attack and prevent leaking. Like, the chamber can be made of glass (in which acids are usually kept) and the nip can be made of galvanized/electroplated iron.

Or if there is still more, we can just make this into a thought experiment.


texts: Peroxide effect in reagents apart from HBr and CHCl₃

texts: Is the peroxide effect observed only with addition of hydrogen bromide and chloroform? If so, why not with other reagents in electrophilic addition on alkenes?


texts: About how much carbon monoxide is produced in these two different reations?

texts:
The U.S. Department of Agriculture produces a gas cartridge to poison subterranean rodents.  The product is provided as a cardboard tube sealed at one end and then loaded with a mixture of 144.6 grams of the following ingredients:

53.0% Sodium Nitrate
28.0% Charcoal
19.0% Inert Ingredients

Once filled, the cardboard tube is sealed at the other end with a thin cardboard cap which can be punctured and a fuse inserted when ready to be used.  The gas cartridge's advertised function once lit is to generate a large volume of carbon monoxide that kills the rodent within a few minutes in its burrow.  My experience has been it is very effective when used according to the instructions.

The USDA gas cartridge is getting harder to obtain anymore and a commercial producer sells a similar product which is utilized in the same applications.  But it is smaller and uses a somewhat different formulation.  It does not advertise how the rodent is poisoned, so I don't know if the resulting gas from combustion is primarily CO or something else.  My experience has been that it doesn't seem to be as effective as the USDA gas cartridge, but I don't know if it is because of its different formulation or just its smaller size.  The 56.7 gram mixture of ingredients in this commercial gas cartridge are as follows:

50.0% Sodium Nitrate
38.0% Sulfur
9.0% Charcoal
3.0% Inert Ingredients

The question is how much carbon monoxide is generated by each of these cartridges when their ingredients are ignited and what are the quantities of other resulting gases?  Just straight theory here is good enough for me.  I know there are probably variables such as how well the ingredients are ground and mixed and what are used as the inert ingredients in each.  But lets just leave those variables out of the equation.


texts: Determine the structure for C6H13Cl using the following data.

texts:
The H NMR for C6H13Cl states that there are 3 different types of protons:

6H, triplet
4H, quartet
3H, singlet

What will the structure look like?


texts:
I found this build-plan recycling on the internet (I believe it was originally published in a book written by the infamous clandestine chemist Hobart Huson) which seemed interesting to me. I do not have the money to pay for a professional fume hood, nor do I have the space to fit such thing. I have to switch the function of my work workplace sometimes because of lack of space (it is also used for woodworking, another hobby of me), so a simple demountable fume hood would be ideal. As said, I found this one with a simple build description, but I was wondering about its effectiveness and safety.

As shown on the picture, the fume hood consists of a demountable frame, a thick plastic sheet covering the frame that is attached to a tube, and a simple exhaust system connected to an other tube that is placed outside the building, so that the fumes can diffuse in the atmosphere. The following four points concern me:

Is the thick plastic sheet enough the prevent most fumes from diffusing in my workplace?
Is this plastic sheet a potential danger in case of fire? Is there some fire resistant (at least until I'm able to pull my fire blanket) plastic sheet that should (must) be used?
Should I be worried about damaging the environment with these exhaust fumes as there is no filtration in this system? Or is reading the MSDS (i.e. the environment section) for the chemicals being used enough?
There is said nothing about the necessity of an explosion proof fan in the build instructions. To what extend should I worry about this when sucking off flammables?

Take note of the fact that we are talking about amateur chemistry here. There are some nasty fumes that need to be removed, like chlorine for example, but no dense fogs of hydrogen cyanide or phosgene.


texts: Why aren't there 8 double bonds in octasulfur (S8)?

texts: I know that the $\ce{S8}$ molecule contains 16 pairs of lone electrons. My teacher always says that we must try to reduce the no of lone pairs, so, had there been double bonds between 8 atoms of sulfur then the no of lone pairs would be reduced. Then why aren't there any double bonds?


texts: How dried up detergent water led to precipitation of snowflake like shapes?

texts: I forgot to drain the water off the bucket (after cleaning stain from a piece of clothing with detergent) and left it for few days. After few days when I needed it back, I found these glittery very small snowflake like shapes at the bottom. Pardon if it's very basic thing, I haven't studied chemistry after school. Thanks for the help.


texts:
The question I have been given is:

  Silver atoms in a metallic lattice only fill up $88\,\%$ of the space ($12\,\%$ is empty). The density of silver is $10.5\ \mathrm{g\cdot cm^{-3}}$. Assuming that silver atoms are hard spheres ($V=\tfrac43\cdot\pi\cdot r^3$, when $r$ is atomic radius), what is the radius of a silver atom? Give the answer in units of $10^{-12}$ meters.

The atomic mass of $\ce{Ag}$ is 107.8682.

My solution:

$$V=0.88\times V$$

$$V=\frac{0.88\times10.5\times6.022\times10^{23}}{107.8682}=5.158\times10^{22}\ \mathrm{cm^3}$$

$$V=\frac43\cdot\pi\cdot r^3 \Rightarrow r=\left(\frac34\cdot\frac V\pi\right)^{1/3}$$
Then I switched to the $10^{12}$ meters, the result was $4.953\times10^{17}$ and it is not correct. What am I doing wrong?


texts: Why does shampoo lather much more the second time it is applied?

texts: When I shampoo my dirty hair, the first time it does not lather very much. The second time it lathers a lot. Why is this?


texts: How do I find molar mass using gas laws?

texts:
A gaseous sample of a compound has a density of $\pu{0.977 g/L}$ at $\pu{710.0 torr}$ and $\pu{100.00 ^\circ C}$. What is the molar mass of this compound?

When I worked the problem I got $\pu{29.9 g/mol}$ is that right?


texts: Does an axis of symmetry determine chiralty?

texts:
What I've understood about chirality and elements of symmetry:

A molecule that is not superposable on its mirror image is said to be chiral.

Plane of symmetry:
An imaginary plane cutting a compound into two symmetric halves.
Any compound possessing it is achiral, so any compound without it is chiral?

Axis of symmetry:
I have never spent so long trying to understand a concept.
An axis of symmetry is an imaginary axis around which by rotating through a minimum angle of rotation, the original compound is obtained.

1. Any compound, be it chiral, achiral or dissymmetric, can have an AOS.

2. You cannot say a compound is achiral just because it has an AOS.

3. Unless, I just had a thought. If on rotation it gives the same compound, making it superposable with the original, thereby making it achiral.

However, wouldn't all compounds (chiral or achiral) on rotation through a particular degree give back the same compound?
Please tell me if everything I've mentioned is right.


texts: Can oxygen gas in air react with Mn3O4 to form MnO2?

texts:
I think $\ce{MnO2}$ at high temperature can be used as a catalyst for $\ce{SO2 + O2 -> SO3}$:

$$
\begin{align}
\ce{MnO2 + SO2 &-> MnSO4}\tag{1}\\
\ce{3 MnSO4 &-> Mn3O4 + SO2 + 2 SO3}\tag{2}\\
\ce{Mn3O4 + O2 &-> 3 MnO2}\tag{3}
\end{align}
$$

I think the first two reactions are possible, but I don't know about the third one.


texts:
An aqueous solution of soluble salt $\ce{B2X}$ has concentration of 0.1 M.
Given data :

  $\ce{K_b(BOH) = 2 × 10^{–5}}$

  $\ce{K_{a1}(H2X) = 2 × 10^{–7}}$

  $\ce{K_{a2}(H2X) = 5 × 10^{–10}}$

What is the pH of the solution?

My attempt,

$$\ce{B+ + X2- -> BOH + HX-  \,\,...      (1)}$$

The hydrolysis constant of $\ce{HX-}$ comes out to be about $10^{-7}$, so I decided to neglect it (is this correct?)

$$Kh=[HX-][BOH]/[X2-][B+]$$

So  the  value  of  $$\ce{K_h=\frac{Kw}{K_{a2}*K_b}}$$

Upon substituting the values I get the Kh=1..(something i have never seen before)

So this means that for the reaction

$$\ce {B+ + X2- -> BOH + HX-}$$

We will end up with 0.05M of $\ce{B+}$ , 0.05M of $\ce{of X2-}$, 0.05M of $\ce{BOH}$ , and 0.05M $\ce{HX-}$ if we start with 0.1 M of $\ce{B+}$ and 0.1 M of $\ce{X2-}$

Now, I do know that

$$\ce{pH=7+\frac{pK_a + pK_b}{2}}$$

I also know that this is true when the hydrolysis constant is smaller than 1. Therefore I cannot use if for this problem.

(Nevertheless, I disregarded this and just used it. I got the answer to be 9.305)

So I am stuck over here.

I got another idea.

When I now look at the sum, the resulting solution looks like a mixture of two buffer solutions,

Buffer 1: $\ce{BOH/B+}$

Buffer 2: $\ce{HX-/H2X}$

I don't know whether this observation is correct. Even if it is correct, I am not sure whether it be used to solve the problem.


texts: Relationship between electronegativity and atomic radius

texts:
Would someone please explain in detail the relationship between the two? I understand that atomic radius is related to ionisation energy but I can't see how atomic radius may be related to electronegativity.

And it appears that they are not inversely proportional to each other, but I couldn't find any explanation for this (or for the relationship between the two) online.

I'm a sixth form student (the equivalent of high school in the US I suppose).


texts: What are some examples of a clear, liquid, UV photoactive polymer?

texts: Something that is not reactive to lesser wavelengths of light, specifically IR.


texts: Reaction between a vinegar/salt/hydrogen peroxide mixture as an etching solution and copper

texts:
I am looking for the less harmful chemical solution to serve as an etching solution. After many searches, my interest went to a vinegar/salt/hydrogen peroxide solution.

I have to ask then if the residue of this solution is harmful and if it is ok to pour it in the regular water waste system.


texts:
I am considering a suspension of a fine powder in a high-viscosity liquid.  The suspension shall be stable over long time scales, i.e. the particles only move a few mm per year, and I have the following boundary conditions:

The particles sizes shall be between 0.1 and 1.0 microns, so the suspension is colloidal
The concentration of dispersed particles in the medium is high (the phases have approximately equal volume).
The viscosity of the medium must be high. I am considering >10000 cSt, which is comparable to thick honey or shower gels
The medium will also be free of water; possibly long hydrocarbons

In a first naïve treatment with Stokes' law I thought that such a suspension should be sufficiently stable. Then I read about interparticle effects, which can lead to agglomeration of the particles and sedimentation (mainly on wikipedia). I don't know yet which material will be used as the solid powder, so I have to consider the worst case of attracting forces between the particles, so that there will be agglomeration and sedimentation in my case. This has to be prevented, but for several reasons I would like to avoid steric stabilization.

However, all examples of agglomeration considered a "thin" liquid like water, while polymeric stabilization technique is based on long polymer chains in the medium. Since in my case the viscosity of the medium is very high in my case, I wondered if this might be enough to prevent agglomeration. The high viscosity is due to long molecular chains, so I'm thinking that this might count as a case of polymeric stabilization. Is it possible to prevent agglomeration and sedimentation of microparticles just by increasing the viscosity of the medium?


texts: Why do Cp2Mg and NaCp complexes turn pink when oxidized?

texts:
I am just wondering why the complexes sodium cyclopentadienide ($\ce{NaCp}$) and cyclopentadienyl magnesium ($\ce{Cp2Mg}$) turn pink when oxidized?
Where does the pink color come from?


texts: pKa of Tris corrected for ionic strength

texts:
I have a question regarding the molar fraction calculation of Tris buffer at different temperatures.

Tris dissociates according to the following equation:

$$\ce{Tris + H2O -> Tris+ + OH-}$$

So, in order to calculate the amount of $c(\text{Tris}^+)$ and thus the amount of strong acid needed for titration, one needs to use derivation of Henderson-Hasselbalch eq.:

$$\mathrm{pH} = \mathrm{p}K_\mathrm{a}' - \log_{10}\left(\frac{[\text{Tris}^{+}]}{[\text{Tris}]}\right)$$

However, $\mathrm{p}K_\mathrm{a}'$ is $\mathrm{p}K_\mathrm{a}$ corrected for ionic strength ($I_c$) at a certain temperature.

The correction of $\mathrm{p}K_\mathrm{a}$ is done via the Debye-Hückel eqation:

$$\mathrm{p}K_\mathrm{a}' = \mathrm{p}K_\mathrm{a} -0.509\times\left| z-z^{+}\right| \sqrt{I_c}$$

Now, for Ic itself one needs to calculate the molar fraction of $[\ce{Tris+}]$:

$$I_c = 0.5\times \left([\ce{Tris+}] + [\ce{OH-}]\right)$$

which requires the use Henderson-Hasselbalch equation making this problem somewhat circular. or am I missing something?


texts:
I've learned about anti and gauche conformations throughout my scholastic journey, and I have heard often that straight-chain alkanes always adopt an all-anti conformation in their lowest energy state. I also know that, in a pure sample of any given straight-chain alkane, (eg. hexane) the anti and gauche conformations are in a certain equilibrium with each other, And that this ratio of gauche to anti shifts towards gauche as the available energy of the sample (i.e. temperature/heat/ pressure) approaches infinity.  My question is as follows: Has anyone in the scientific community to date successfully forced an entire sample of straight-chain alkanes into the all-gauche conformation without significantly raising the conditions above STP? I have scoured the internet but have not surfaced with a definitive answer, so I now turn to the scientific community.

All contributions are greatly appreciated.


texts: Are there any sources that could provide Ksp value thresholds for things that are "completely soluble", "partially soluble", and "not soluble"?


texts: Do I really need 4 different water treatment systems with this water analysis?

texts:
We installed an artesian well and we had some surprises. We asked a few places around and they all told me that we needed 4 different systems to solve our water problem. I am ready to accept this fact but before having our basement transformed to a factory I just wanted to confirm that this is the only solution.

Here is the result of my analysis.

The problems are:

Barium  $6.9 \:\mathrm{mg/L}$    (2nd analysis revealed same results)
Apparent Color 17.5 UCA
Iron  $0.47 \:\mathrm{mg/L}$
Total sulfur $0.07 \:\mathrm{mg/L}$

Also the water is hard ($210 \:\mathrm{mg} \ce{CaCO3}/\rm L$) which is not recommended

My question is, do I really need 4 different systems to treat my water?


texts: Can someone tell me why β-sitosterol has the beta prefix? What is it denoting? When comparing its structure to other similar phytosterols I see no need for it.


texts: How does a mixture not retain its chemical identity?

texts:
My book says that matter can be classified as an element, compound, or mixture. It further says that a pure substance (or substance) is matter that has distinct properties and a composition that doesn't very from sample to sample. So far, so good. Then it says that

  all substances are either elements or compounds

An element is one type of atom (something that "cannot be decomposed into simpler substances") and a compound is composed of two or more elements; these both clearly are substances. Then, it says that

  Mixtures are combinations of two or more substances in which each substance retains its chemical identity.

This is where I'm confused. How are mixtures not substances? They have distinct properties, and their composition doesn't vary from sample to sample, if you set a standard for the sample. You can create any arbitrary mixture, and you can create any arbitrary compound, and if you follow the "recipe" for either you will always get the same thing, as far as I know.

Where is my logic flawed?


texts: How to determine gerade & ungerade symmetry of a MO orbital?

texts:
J.D.Lee writes in his book Concise Inorganic Chemistry:

  [...] An alternative method for determining the symmetry of the molecular orbital is to rotate the orbital about the line joining the two nuclei and then rotate the orbital about the line perpendicular to this. If the sign of the lobes remains the same,  the orbital is gerade, and if the sign changes, the orbital is ungerade.

Now, it can be detected easily which MO, formed due to the overlapping of s-s or p-p orbitals, is gerade or ungerade as shown in these pics:

But what about the molecular orbitals formed due to the overlapping of s-p orbitals or p-d orbitals?
mo due to to overlapping of s-p orbitals:

mo due to overlapping of p-d orbitals:

If I rotate about the first orbital about an axis perpendicular to the inter-nuclear axis, the smaller lobe goes to the right only; the sign always remains same; just the position of the lobe has been changed. But in the first picture, only the bonding mo is gerade while the anti-bonding mo is ungerade; I'm not getting how by rotating along the axis perpendicular to the inter-nuclear axis, the sign of the antibonding mo changes making it ungerade.

Can anyone please help me how to apply the procedure for the molecular orbitals formed due to the overlapping of s-p & p-d orbitals?


texts: Is it possible for a compound to be soluble in a mixture of solvents but not the individual solvents?

texts:
Some weeks ago one of my friend needed to use turpentine. As a good but ignorant chemist on that point I did some research about it. I found (at the beginning) in the French wikipedia page of turpentine :

  "L'essence de térébenthine est un mélange de molécules variées,
  comprenant en particulier des terpéniques, des acides et des alcools.
  Ce liquide est insoluble dans l'eau, dans l'alcool absolu et dans
  l'éther, cependant il est légèrement soluble dans un mélange
  eau-alcool."

Which translated in English gives,

  "Turpentine is a mixture of different molecules, particularly terpenes, acids, and alcohols. This liquid is insoluble in water,
  absolute alcohol, and ether, but it is slightly soluble in a mixture of
  water-alcohol."

I found no reference about that. Is it really possible? It sounds particularly strange to me. And obviously if that is possible, how?


texts: Do maxima in Gibbs energy also correspond to equilibrium positions?

texts:
ΔrG=(∂G/∂ξ ) at constant p and constant T, where ξ is the extent of reaction.

By Second Law implication, ΔrG= 0= (∂G/∂ξ ) at equilibrium. If we consider a graph of G against ξ, this would mean  we have a turning point (where first derivative=0) when ξ is that extent of reaction when equilibrium attained:

  (∂G/∂ξ )= 0 when ξ= extent of reaction until equilibrium
  attained

So, ΔrG=0 when equilibrium attained.

However, first derivative=0 does not mean minimum point only, it can mean maximum point too! Let's say you do work until you reach Gibbs energy maxima. My question: Does a Gibbs energy maxima correspond to equilibrium state or not?

(a) If yes, doesn't this violate the Second Law which implies that Gibbs energy should be minimized whenever possible? No matter which direction you move, your Gibbs energy will always decrease. Just simply move from the maximum point and you will at least be better than your current state:

(b) If no, then it will mean that we have to move from the maximum point, but in which direction? In case the graph is a symmetrical parabola, where same dξ results in same dG, what will you observe in real life? Shift to reactants or products?


texts: There is a way to classify oxides according to their behavior where we have the following categories: Acidic, Basic, Amphoteric and Neutral. But is there a way of classifying the oxides according to their chemical bond?


texts:
Below is a chemistry practice problem.  I am curious why the change in heat of the oxygen molecules doesn't affect the calculations.

  Methylhydrazine ($\ce{CH6N2}$) is commonly used as a liquid rocket fuel. The combustion reaction is below. When 4.00 g of methylhydrazine is combusted in a calorimeter, the temperature increases from $\pu{25.00 ^\circ C}$ to $\pu{39.50 ^\circ C}$.  The calorimeter constant is $\pu{7.794 J/^\circ C}$ and the specific heat of methylhydrazine is $\pu{2.93 J/g ^\circ C}$. What is the overall heat of the reaction (kJ/mol methylhydrazine)?

$$\ce{2 CH6N2(l) +   5 O2(g) -> 2 CO2(g)+   2 N2(g) +   6 H2O(g)}$$

$$\begin{align} \mathrm{molecular\; mass\;\;} \ce{CH6N2} &= \pu{46.08 g/mol}\\
\rightarrow \pu{4 g} \cdot \pu{1 mol}/\pu{46.08g} &= \pu{0.0868 mol} \ce{CH6N2} \\ \rightarrow
 q &= (\pu{4 g})(\pu{39.5 ^\circ C} - \pu{25 ^\circ C})+(\pu{7.794 J/^\circ C})(\pu{39.5 ^\circ C} - \pu{25 ^\circ C}) \\  &= \pu{283 J}  \\ \rightarrow \Delta H &= \pu{-3.26 kJ/mol} \end{align}$$

The change in heat accounts for the $\Delta T$ and temperature change of the calorimeter and the temperature change and $C_p$ and mass of the methyl hydrazine, but why doesn't the oxygen also absorb heat in accordance with its mass and specific heat constant?

-3.26 kJ/mol is the "correct" answer in the answer key, meaning that the absorption of heat by methylhydrazine IS required to get the answer which I didn't expect-I though it would just be the heat absorbed by the calorimeter, but I understand why the methylhydrazine would absorb heat from the reaction, but then why doesn't the oxygen absorb heat since there is actually more mass of oxygen in the calorimeter as mass of methylhydrazine.


texts: Difference between Superheated steam and Superheated water?

texts:
I'm working on a project (school level) and in it I'll be dealing with the pressure generated by water when superheated.

I could understand the concept of superheated water but superheated steam is hard to understand. Are both inter-related, i mean that when water is superheated then it changes into superheated steam?

Or is it something different? And since in my project I require high-pressure-energy to be generated from water, so which one will be better, superheated steam or superheated water?


texts: In Parent chain choosing should one consider longest chain or chain with more substituents?

texts:
Should one take the longest chain or the one containing the prefix/suffix with most priority.Moreover if a shorter chain has two units of the main prefix will it be taken as parent?

examples:

2-ethyl butanoic acid or
3-carboxy pentanoic acid


texts: Which is more amphoteric: zinc or copper hydroxide?

texts:
$\ce{K_{a} ~Cu(H2O)_6^2+}{=~5*10^{-7}} $

$\ce{K_{a} ~Zn(H2O)_6^2+}{=~2.5*10^{-10}} $

Given this information, which forms a more amphoteric hydroxide?

My reasoning is that copper hydroxide is more amphoteric than zinc hydroxide. My reasoning is that because $\ce{K_{a} ~Cu(H2O)_6^2+}$ > $\ce{K_{a} ~Zn(H2O)_6^2+} $, $\ce{Cu(OH)_2}$ should be more amphoteric because it will probably have the bigger $\ce{K_{a}}$. This fulfills half of the definition of amphoteric - behaving as both an acid and base.

But how do I compare the base strengths of $\ce{Zn(OH)_2}$ and $\ce{Cu(OH)_2}$? I need to, because being amphoteric means the substance acts as both an acid and a base!

Consider the following:

$1. ~{K_{a1}:} ~\ce{Cu(H2O)_6^2+ + H_2O -> Cu(H2O)_5(OH)^+ + H_3O^+}$

$2. ~{K_{a2}:} ~\ce{Cu(H2O)_5(OH)^+  + H_2O -> Cu(H2O)_4(OH)_2 + H_3O^+}$

$3. ~{K_{a3}:} ~\ce{Cu(H2O)_4(OH)_2  + H_2O -> Cu(H2O)_3(OH)_3^- + H_3O^+}$

Basic character of copper hydroxide is illustrated by the below equation:

$4. ~\ce{Cu(H2O)_4(OH)_2  + H_2O -> Cu(H2O)_5(OH)^+ + HO^-}$

The above equation, reversed, is:

$5. ~\ce{Cu(H2O)_5(OH)^+ + HO^- -> H_2O + Cu(H2O)_4(OH)_2 }$

This equation is very similar to $~{K_{a2}}$ except that the base is hydroxide ion instead of water.

We can write a similar equation for zinc hydroxide:

$6. ~\ce{Zn(H2O)_5(OH)^+ + HO^- -> H_2O + Zn(H2O)_4(OH)_2}$

Let's compare equations $5$ and $6$. We can expect $5$ to be a larger extent reaction than $6$ because hydrated copper ion is a stronger acid than hydrated zinc ion to start with. So:

${K_{rxn5} > K_{rxn6}}$

And therefore,

${K_{rxn4} < K_{rxn7}}$

$7. ~\ce{H_2O + Zn(H2O)_4(OH)_2 -> Zn(H2O)_5(OH)^+ + HO^-}$


texts: Why is only the carbonate anion used to precipitate Barium?

texts:
Q: Why is the $\ce{CO3^2-}$ anion used to precipitate Barium from $\ce{BaBr2}$ and not another anion, such as $\ce{PO4^3-}$, or $\ce{SO4^2-}$?

I am studying high school Chemistry, and the current unit is precipitations. The worked example states that $\ce{Na2CO3}$ can be used to precipitate $\ce{Ba^2+}$ from a solution of $\ce{BaBr2}$, which makes sense.

However, it does not explain why the $\ce{CO3^2-}$ anion should be selected, when according to the solubility table $\ce{SO4^2-}$ and $\ce{PO4^3-}$, would both be able to precipitate $\ce{Ba^2+}$ from $\ce{BaBr2}$. Am I missing something obvious? Why is it that the $\ce{CO3^2-}$ anion is favoured over the other two anions?
`


texts: Does variations in air pressure affect the melting point of PLA and ABS while 3D Printing?

texts:
Tight temperature controls are needed to ensure that the filament used in fabrication does not begin to "ooze". In places where the air pressure rises and drops during the course of the day there may be more or less ooze taking place. Controlling ooze is paramount to obtain better print quality.

Question: Given Boyle's law, shouldn't the melting point of PLA and other plastics used in the Fused Filament Fabrication 3D printing methods change based on the ambient air pressure of the machine's location? Should air pressure be taken into account when calculating how much heat to apply to the print nozzles? Does humidity affect PLA's melting point?


texts: I’m doing a research project which involves rubber toughening - the particular example I'm looking at is the toughening of SAN polymer (styrene-acrylonitrile) with polybutadiene to make ABS. What I'm looking for is a description of why the process makes the material tougher, whereas everything I can find online seems to be research about the effects of different factors on the toughness. If anyone could provide a source that would be great.


texts: Formulas for non-bonded interaction energies

texts:
If one were to calculate the non-bonded interaction energy between two atoms, this would equate to the sum of the vdW + electrostatic potential energies:

$$
E_{\text{non-bond}} = E_{\text{vdW}} + E_{\text{electrostatic}}
$$

Could anyone please explain how I could calculate these potentials providing a formula?

Perhaps given an example with zinc ($\ce{Zn^2+}$) and oxygen ($\ce{O}$), where $\sigma$ and $\varepsilon$ values (defined by Charmm27) are given as:

\begin{array}{ccc}
\hline
\text{Species} & \sigma & \varepsilon \\
\hline
\ce{Zn} & 1.942 & 0.25 \\
\ce{O}  & 3.029 & 0.12 \\
\hline
\end{array}

Ultimately I just wish to understand how they are calculated.

Simply put, I am trying to calculate non-bonded interaction energy between a ligand and a protein. However, after trying to understand each of these terms I am a little lost.


texts: Why there is no change in water level when salt is added?

texts: Let us say we have one glass of water and after that when we add one or two spoon of salt then we notice that salt dissolves in it but when we measure the water level we found that there is no difference between initial reading and final reading. So what's happening over there ? Why water level doesn't changed when salt is added ?


texts:
I have faced this problems when I was working in lab with hexane for the first time.

I was trying to guide dispersion of nano-particles in hexane solution to a fluid cell (vacuum chamber) with a syringe and a flexible tubing (about 2mm or 3mm diameter). All the materials that I use are hexane resistant.
The fluid cell is kept on very low pressure, so the goal is not to have any bubble formed in it.
When I inject hexane fluid, midway before it reaches the chamber, the vapor bubble are formed ( I think because of low boiling point of hexane ) , which is bad I don't want any bubbles go in the chamber.
However, I figured that if the flow is not horizontal or parallel to the ground (i.e when i inject vertically up ward to chamber) I can avoid the bubble flow.

I also thought to do the injection process fast, however the whole flow has to be very slow for the experiment.
 I would like to know what exactly causing it and what are your suggestions to avoid the bubble formation in a horizontal flow.

I was thinking maybe adding some other solution with higher boiling point would be a case to avoid it. But I don't know exactly what solution. And also it is important to keep in mind that hexane solution contains magnetic nanoparticles and I don't want any effect (like aggregation and so on) of added solution into the dispersion nanoparticles.
Thank you,


texts: How is the energy of reactants in a chemical reaction found ?

texts:
A pretty rudimentary question, but I'm reviewing the concept of energy diagrams and activation energy and I'm curious to know how chemists find the energy of reactants and of a transition state in a laboratory.

What kinds of instruments are used ? As well, aren't transition states only something we can imagine ? So how is it that chemistry are able to find their energy in a lab ?


texts: How do you know if a nucleophile is strong enough to to break a bond?

texts: For instance, iodine can displace bromine in $\ce{CH3Br}$ Is this due to iodine being lower in the periodic table, thus having more electrons in the outer shell and being a stronger nucleophile?


texts: What effects would an electron in the nucleus have?

texts:
Under the understanding of quantum chemistry:

  There is a very miniscule chance that an electron could appear inside the nucleus of an atom.

What could possibly happen if this "phenomenon" were to occur?  Would it wreak havoc upon the atom and tear it apart?  Or will it bind with the protons and create a temporary vacuum?

Under my current research, the electron would jump out of the nucleus as soon as possible because this phenomenon should not occur for more than a fraction of a second. Though it shouldn't leave without some adverse effects.


texts: Reaction between phenylamine and halogens

texts:
I understand that phenylamine is considerably more reactive than benzene, meaning that it is able to react with bromine water to give 2,3,6-tribromophenylamine. But I was then wondering why I haven't seen anywhere mention reactions with other halogens. So will phenylamine react with other halogens to produce a similar compound, I see no reason why it wouldn't happen? Do text books just use bromine water as it is convenient?

Will  $\ce{C_6H_5NH_2 + 3Cl_2 -> C_6H_2NH_2 Cl_3 + 3HCl}$ happen?


texts: Debye-Huckel theory with non-polar solvents

texts:
I want to calculate the activity coefficients of mixed solvent salt solutions. I am seeing very strange behavior when I try calculating the activity coefficient of salts in non-polar solvents using Debye-Huckel theory though and its messing up my down-stream calculations.

In a simple example, let's compare the activity of NaCl in hexane and water:

Inputs: (hexane / water)

Density: 654 / 1000 kg/m^3
Dielectric constant: 1.89 / 80.4
Temperature: 293 K
Molarity = 0.1 mol/L

Calculations:

$A = consts \frac {\sqrt {\rho}}  {(\epsilon * T)^{1.5}} = $ 230 / 1
$I = \frac12 \sum_{ions} cz^2 =$ 0.1 / 0.1
$ln(\gamma) = -Az^2\sqrt I = $ -73 / -0.32
$\gamma = 10^{-32}$ / 0.72

In equilibrium the salt activity should be the same in each phase, $\gamma_{aq}x_{aq} = \gamma_{org} x_{org}$, which would imply that the salt should all be flying over to the organic phase. That clearly makes no sense.

Why does this give such totally wrong behavior in a limiting case?


texts: Hybridisation of Mn in potassium permanganate

texts: I'm clear with the concepts of crystal field theory. But I can't figure out the exact reason why the hybridisation of manganese in potassium permanganate ($\ce{KMnO4}$) is $\mathrm{d^3s}$. Can anyone explain please?


texts: Can the titrant and the unknown material be flipped?

texts:
We know the typical experiment of determining the concentration of $\ce{Fe^2+}$, where we titrate $\ce{MnO4^-}$ which has dark purple color and watch the color of the bottle.

Can we also determine the $\ce{MnO4^-}$ concentration using $\ce{Fe^2+}$ as titrant and how?

You can see that the iron is inside the beaker and we titrate with  $\ce{MnO4^-}$. Can we do it backward, i.e. having $\ce{MnO4^-}$ inside the beaker with purple color and we titrate $\ce{Fe^2+}$.


texts: Is the heat of reaction always negative?

texts:
For example, I have a question below that I know the correct answer to, but I don't know why it's positive rather than negative.

When $\ce{NaOH}$ is neutralized by $\ce{HCl}$:
$$\ce{NaOH(aq) + HCl(aq) + H2O(l) -> NaCl(aq)}\qquad{\Delta H = \pu{-56.2kJ/mol}}$$
How much heat is produced when $\pu{195 mL}$ of $\pu{0.667 M }\ce{NaOH}$ are mixed with $\pu{125 mL 1.750 M }\ce{HCl}$?
a. $\pu{−14.6 kJ}$
b. $\pu{14.6 kJ  }$
c. None of these.
d. $\pu{7.31 kJ}$

I know that the answer is (d), but I'm not sure why it is correct. I thought the correct answer was $−7.31$, but there was no answer choice for $−7.31$.


texts: How do we explain mutations, in the deterministic world of chemical reactions?

texts:
I'm not a chemist, neither a molecular biologist. But I'm fascinated with science.

The way I understood, DNA is a macro-molecule which is made of atoms. And in reproduction, either mitosis or meiosis then mating, or in RNA creation mutation can happen. And mutation means a letter molecule in the chain of DNA can become another letter.

From the other side I know that by combining a known set of reactants, we get the same products, ALL the times. In other words, chemical reactions are deterministic and no matter how much we try, H2 + O results in water, and not in solphuric acid for example.

At this point I'm stuck. And I can't find an answer. How mutation happens in DNA while it's the outcome of chemical reactions and those reactions are deterministic?


texts: Synthesis of mandelic acid from benzaldehyde

texts:
For an upcoming exam, I have to describe the synthesis of 2-hydroxy-2-phenylacetic acid (mandelic acid) from benzaldehyde. The provided answers describe quite a long process, consisting of 8 stages. However, I've been suggested a much simpler method, consisting of:

$\ce{C6H5CHO + HCN -> C6H5CH(OH)CN}$
$\ce{C6H5CH(OH)CN + HCl + 2H2O -> C6H5CH(OH)COOH + NH4Cl}$

This is even simpler than the 3-stage process described in the Wikipedia article. Could it be a viable answer?


texts: Number of water molecules in a box to simulate liquid water

texts:
I have seen that depending on the simulation approach, different number of water molecules are employed for studying liquid water properties.

32 in early DFT calculations
The electronic structure of liquid water within density-functional theory
The Journal of Chemical Physics 123, 014501 (2005); https://doi.org/10.1063/1.1940612

216 in early classical molecular dynamic simulations

Molecular Dynamics Study of Liquid Water The Journal of Chemical Physics 55, 3336 (1971); https://doi.org/10.1063/1.1676585

256 I'm not sure if this number of water molecules is just for computational reasons $2^8$= 256

So I'm wondering, What is the reasoning behind them?,

Edit:
In other words, If I want to obtain the ambient density of the system and I don't know anything about it (number of  molecules or the size of the simulation box, assuming cubic), what should I do?

As a starting point, the only thing I know is that the size of the simulation box should be chosen considering a number density that corresponds to the experimental density of the system.


texts: IR spectroscopy in CCl4 Solution v/s Liquid film

texts: Why there are differences in these spectra ? Which one is more useful and accurate ? What is the significance of using these two different methods ?


texts: Retention of surface texture after combustion

texts:
Just some while ago I was burning a box of cardboard in my backyard and I saw a very curious phenomenon.

I saw that as the cardboard box started burning it started to curl.  Up after a while as I came back to check if the fire was out I saw that though the cardboard box wasn't a box any longer but individual sides/faces of the box had retained their ridges and texture though they had tuned greyish white and crumbly.

My questions:

Why did the cardboard start to curl up as it began to burn?
Why did it retain its texture if not shape and size?


texts:
Why do Rydberg atoms have electrons that can transition above the first ionization energy?
This can only happen in a multi-electron system but I don't see how the Rydberg formula would even work for n = infinity + 1. I thought it might have to do with the second ionization energy but the definition of that is just another electron being ionized not anything above the first ionization energy.


texts: How will metallic lithium react with atomic oxygen?

texts:
Very high in Earth's atmosphere, there's a lot more atomic oxygen than anything else. Although I'm sure the energies involved in keeping oxygen in this state are an important variable, I'm interested (for now) in what compounds would form.

Mistake here: should be targeting $\ce{Li2O}$, not $\ce{LiO2}$. Would you get $\ce{LiO}$, then $\ce{LiO2}$? If so, will $\ce{LiO}$ be stable enough to bond with another $\ce{O}$ atom later? I can easily believe that lithium metal will simply erode away faster than a film of oxide could develop, given temperatures in the thermosphere and above. I just haven't seen much chemistry on this, however.


texts: What is meant by 'electrons of like/unlike rotation'?

texts:
Explaining the reasons behind electron repulsion,
Radiochemistry asserts that,

  Interelectronic repulsion in related not just to electron pairing, but also to [the] angular momentum of the electrons. [---]

  e.g., in $\ce{Pr^2+ (4f^3)->Pr^3+ (4f^2)}$ ionisation removes repulsion between [electrons] of like rotation [---]

  $\ce{Pm^2+ (4f^4)->Pm^3+ (4f^3)}$ ionisation removes repulsion between [electrons] of unlike rotation [---] [emphasis added]

What exactly is meant by 'electrons of like/unlike rotation'?

You may glance at these links, but only if you want to.

Why don't we see these lanthanide species?
Howcome orbitals become 'core-like' when electrons are removed?
What's up with this quarter / three-quarter rule?

Original topic: Predominance of III oxidation state for lanthanides


texts:
I've been trying to make Sodium dichromate $\ce{Na2Cr2O7}$ by following these steps:

Dissolve an inox spoon in $\ce{H2SO4}$
Filter the solution
Dissolve the obtained sludge in $\ce{NaClO}$
Heat the solution until slurries appear
Filter the solution

The solution I obtained was yellowish (light yellow), I tried to add some acid to see the orange color of the (hypothetical) dichromate but nothing happened!

I added some ammonia before acidifying the solution, nothing as well.

1st: Is this method the right one to obtain chromate/dichromate?
2nd: If yes, why didn't the orange color appear?


texts: According to this textbook, H₂O has lower reduction potential (-0.83 V) than Zn (-0.76 V). This mean zinc is unable to reduce water to hydroxide. If so, why this video demonstrate that by heating zinc in water, a reaction occurs producing hydrogen gas from the bubbles while also turning wet red litmus paper blue?


texts: How does the chemical potential allow for open systems to be considered?

texts:
Gibbs free energy can be defined as: $$dG=VdP-SdT+\sum_i\mu_idn_i$$ where $\mu=(\frac{\partial G}{\partial n})_{P,T}$. Last term, $\sum_i\mu_idn_i$ allows for open systems to be considered (where $dn$ does not equal zero). However, this can also be used for state functions like enthalpy too:
$$dH=TdS+VdP+\sum_i\mu_idn_i$$
But my question is why can this be used for enthalpy, considering that $\mu=(\frac{\partial G}{\partial n})_{P,T}$ (i.e it's a partial derivative of $G$ not $H$). Perhaps it's clearer for me to write the total derivative out like this: $$dH=(\frac{\partial H}{\partial S})_{P,n}dS+(\frac{\partial H}{\partial P})_{S,n}dP+(\frac{\partial G}{\partial n})_{P,T}dn$$ where I have considered a single-component open system (the component may enter or leave the system)


texts: In PCl2F3, why are two Cl atoms not on axial position?

texts:
According to these sites:

Chemistry Help

Molbase

in $\ce{PCl2F3}$, both $\ce{Cl}$ and one $\ce{F}$ atom are on equatorial position, and other 2 $\ce{F}$ atoms are on axial position as follows:

The first site mentions that to minimise repulsions of $\ce{F - F}$ bonds. But this structure is in fact increasing the repulsions, and decreasing stability, since the bond angle of $\ce{F - P - F}$ bond will be about $\mathrm{90^\circ}$
If instead all the $\ce{F}$ atoms are on equatorial position, and the 2 $\ce{Cl}$ on axial positions, then the repulsion may be further minimized.
So according to me, the structure should be:

Question: Why is my structure wrong? Please explain. Thank you!


texts:
My textbook says

In the presence of strong base such as KOH and at high temperatures, triple bond at terminal C-atom of higher alkynes migrates to give disubstituted alkyne.Therefore alcoholic KOH is used when rearrangement is not a problem,on the other hand terminal alkynes can be produced using NaNH2 in liquid ammonia as those alkynes essentially donot
rearrange.

Why is that so?I know KOH is not as strong a base as sodamide but why alkynes formed by using it are capable of rearrangement while those formed through sodamide are not?
The product is same in both cases,what its got to do with the reagent?And what is the significance of high temperature?


texts: What are the correct resonance structures of nitrous oxide?

texts:
There was a question in one of my exam papers to draw the resonance structures for $\ce{N2O}$.

These are the ones I drew, but they were not awarded marks:

The ones in the marking scheme are as follows:

Can anyone please explain why mine aren't correct?


texts: Gibbs free energy=potential free energy? (Transition state theory)

texts:
Online I found the plot Gibbs free energy vs. reaction coordinate:

https://en.wikipedia.org/wiki/Transition_state_theory

and on many books I found the plot potential energy vs. reaction coordinate (e.g. page 237 Atkins, Physical Chemistry for the Life Sciences, 2nd Ed).

In the first case activation energy is defined as $\Delta G$, whereas in the second case is defined as difference of potential energy.

Thus is the Gibbs free energy a potential energy?

Thank you very much.


texts: Mechanism of acid-catalyzed Robinson annulation?

texts: My professor posed my organic chemistry class a challenge problem for bonus points and I've been racking my brain over the last three days trying to work it out and I want to know if my solution is plausible. The problem asks us to draw the best curved arrow mechanism for the reaction in the bottom left corner of the photo included in this post (a substituted cyclobutane molecule to a substituted cycloalkene). At first, this seemed like a simple intramolecular Robinson annulation, however it appears to be catalyzed using the hydronium ion, rather than the hydroxide ion. No other reactants are stated, including light, heat, nor a double equivalence of the starting compound. Working through every mechanism that I could think of, I eventually ended up with the solution in the picture below. I assumed that reaction rates and percent yields were unimportant, as long as the mechanism is plausible. Does this solution break any rules of organic chemistry? Is there a better solution?


texts: Understanding strong acid titrated with weak base graph

texts: I don’t understand why the conductivity doesn’t change after the equivalence point. To my understanding, at the equivalence point there is $\ce{NH3}$, $\ce{NH4+}$ and $\ce{Cl-}$ in the solution. As more $\ce{NH3}$ is added it only partially dissociates, thus conductivity stays the same. But doesn’t the concentration of $\ce{Cl-}$ ions also contribute to the conductivity, and its conductivity decreases are more aqueous $\ce{NH3}$ is added as it becomes more dilute? Where is the issue in my understanding. Thanks for the help.


texts: How can we define optical isomerism?What is the example of non enatiomeric optical isomers?

texts:
My book has very vaguely explained these concepts,I can't understand anything from there.
Through a little bit of research on the internet I came to following conclusion:

that optical isomers are either dextrorotatory or levorotatory
all enantiomers are either dextro or levo so they are optical isomers.
Some diastereomers may also be related as d- or l- (though I feel the angle of rotation will be different) and thus can be optical isomers.

I feel I am missing something or have the wrong concept entirely.
These are pics from my book.
In the heading of optical isomers there are 4 isomers of tartaric acid mentioned,why is that?So how many types of optical isomers are there?


texts:
When I was in lower grades, I was taught $\ce{NaOH and KOH}$ are the strongest bases. But I realised later that there can be more stronger ones. After a bit of research on the internet, I found these three to be spoken more about.

Lithium diisopropylamide (LDA)
Methyllithium (MeLi)
Butyllithium (BuLi)

Wikipedia on LDA says that the $\mathrm{p}K_\mathrm{a}$ of its conjugate acid is $36$, which means the $\mathrm{p}K_\mathrm{b}$ value at $\pu{298K}$ is $-22$. (Since $\mathrm{p}K_\mathrm{a} + \mathrm{p}K_\mathrm{b} = 14$).
Likewise, for BuLi and MeLi I found the $\mathrm{p}K_\mathrm{b}$ value to be $-36$ and $-34$ respectively from the $\mathrm{p}K_\mathrm{a}$ values of their conjugate acids. So, can we conclude that BuLi is the strongest base? Is this absolute basic strength defined?

Sources for $\mathrm{p}K_\mathrm{a}$ values:

Wikipedia-LDA
pKa of MeLi and BuLi


texts: Is it correct to say that the pKa is the pH at equilibrium?

texts:
I've heard this said when looking at the charge of certain groups on a molecule (with different $\mathrm{p}K_\mathrm{a}$ values) in a solution of certain $\mathrm{pH}.$ But is that really correct to say?

Based on speciation diagrams, I would have thought that the $\mathrm{p}K_\mathrm{a}$ is always constant and that $\mathrm{p}K_\mathrm{a}$ is simply the $\mathrm{pH}$ at the point where the concentrations of the acid and its conjugate based are equal.


texts: Why is the difference in boiling point so much greater between methanol and methane than it is between 1 decanol and decane?

texts:
So any data sheet will tell you;

Group 1: methane boils at: -164 deg C
         methanol boils at: 65 deg C

Group 2: decane boils at: 174 deg C
         1-decanol boils at 229 deg C

that being said; why is the difference in boiling point so much greater between methanol and methane than it is between 1 decanol and decane ?

As well is there anything else other than difference in non-polarity and IMF's that contribute to differences between molecules in individual groups (i.e. between methane and methanol; between decane and 1-decanol)


texts:
Below is a copy of the method I am using to determine electron configurations.

Question:

  Write the full and short electron configuration for tellurium.

My final answer was:

Full Configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p4

Short: $[\ce{Kr}]~\ce{5s^2 4d^10 5p^4}$

However, checking with google, it seems the answer is actually: $[\ce{Kr}]~\ce{4d^10 5s^2 5p^4}$

Is the silly "follow the yellow brick road" thing faulty? Or is it that order doesn't matter in this situation?


texts:
In electrolysis why do positive ions go to the cathode? Since the cathode is positive, won't the positive ions face repulsion at the cathode and would require more energy?

I understand that reduction happens at the cathode and positive ions reduce but somehow it does not make sense as positive - positive charges repel.


texts: Identify the structure of the compound (C3H5NO) given its NMR chemical shifts

texts:
I am trying to figure out the structure of the compound $\ce{C3H5NO}$ given just the following data from the 1H NMR spectrum:

$\delta 5.8 ~ \text{(singlet, 1H)}; \delta 6.2 ~ \text{(triplet, 2H)}; \delta 7.4~ \text{(triplet, 2H)}$

From 2-2-1 combination I have the following candidates:

Only the first and second one satisfy the multiplet data but I can't understand how their chemical shifts are so high. For a $\ce{-CH2}$ adjacent to $\ce{-C#N}$, the chemical shift reaches the value around $1.3 + 1 = 2.3$ but the given values are almost thrice of it. The $\ce{-OH}$'s proton's value seems fine nevertheless. Can anyone explain the reasoning behind the two other values? Or is the compound I have predicted wrong?


texts:
For mutarotation, at least one hemiacetal group must be present in the
  sugar. Therefore, non-reducing sugars do not show mutarotation.

Why?

Consider the following reaction:

$$\ce{\beta-D{-glucose} + CH3OH + HCl -> \alpha-D{-glucopyranoside} + \beta-{D-glucopyranoside}}$$

Even though the pyranoside has an acetal group, the reaction is still reversible? Therefore, shouldn't pyranoside show mutarotation? Isn't the mechanism for the reversible reaction for acetal same as the one for hemiacetal?


texts: How can I find the Van der Waals constants (a and b) without any critical values?

texts:
I'm given a container of gas that is kept at constant temperature, and whose volume is decreased by applying pressure, from A to E, as the graph shows. I am given the temperature, the total moles in the container, and the following data:
At B the molar volume is 1.153, and the pressure is 17.76.
At C the molar volume is .8167, and the pressure is 17.76.
At D the molar volume is .032, and the pressure is 17.76.

Given this data, and I emphasize, only this data (no critical P, T, or Vmolar), find the van der Waals constants, a and b, for the gas.

I've been working on it for 3 hours and so far all I can come up with is a single equation in terms of a and b at point B: 17.76=RT/(Vmolar-b) - a/Vmolar^2
At point C, the equation would be the same as what I came up with for B, since the temperature and pressure remains the same as B, and we're in the region of co-existence, so Vmolar is at its maximum for the gaseous phase and therefore also is the same as in B (any further increase in Vmolar causes precipitation).

Any and all help is greatly appreciated.


texts: what is mechanism for reaction phenol + dimethylsulphate -> anisole

texts: Dimethyl sulphate breaks the oh bond and forms anisole. How does the reaction proceed?? is it oxygen lone pair attacks on sulphur which has partial positive charge?? the reaction takes place in presence of naoh


texts: Increasing the contract surface area between hydrocarbons raises boiling point, so hexane should have a higher boiling point than propane. This doesn't really make sense to me. What is the difference between pulling apart a pair of propane twice, versus one pair of hexane? Why would the total amount of energy needed differ? It's seems to go against the concept of pressure.


texts: Is it possible to remove sugar from a sweetened drink but without boiling it?

texts: Is it possible to remove sugar from a sweetened drink without boiling it? This might not be a good question but I'm wondering if you could separate sugar from a sweetened drink and replace the sugar for an artificial sweetener.


texts: White growth on unopened bottle of chlorotrimethylsilane

texts: I have a white, moldy-like substance that has been growing near the cap of an unopened glass container filled with TMSCl. It has spread to form a thin, powdery coating on all of the other containers of organic reagents it is stored with. This substance appears to have a corrosive effect on glass, but leaves plastic containers and metal containers unaffected. I'd like to know what it is before I go about cleaning it up.


texts: How could you predict degenerate pi molecular orbitals just knowing what symmetry point group a molecule belongs to?

texts:
If you were to apply the Huckel method to some molecules which belonged to, say, $C_{2v}, D_{2h}, $ and $ D_{4h}$, which ones would you expect to have degeneracies?

I'm not sure if this is mixing up math jargon with chemistry jargon here, but I know the Mulliken symbol E is doubly degenerate and T is triply degenerate. So would the $D_{4h}$ molecule have degeneracies because it has the irreducible representations $E_g$ and $E_u$?


texts: electron donation affecting carbonyl bond strength

texts:
I have been told that electron donation decreases carbonyl bond strength and thus decreases the bond stretch frequency, but electron withdrawal increases it.

This does not seem to make any sense as I presume that increasing electron density between two atoms should increase the attraction of their nuclei to those electrons and thus to each other. Is this reasoning flawed? or does this just apply to carbonyls?


texts: Role of alcoholic potassium hydroxide in an E2 reaction

texts:
Which of the following compound will give least substituted alkene as major product with alcoholic $\ce{KOH}$.
The options are:
1.
2.

3.
4.

I am confused between options 1 and 3. Both seem to give more substituted alkene as the major product. Does alcoholic $\ce{KOH}$ always mean it is an E2 elimination?
What is the mechanism here?


texts: When is the activity coefficient greater than 1?

texts:
I am quoting a sentence from Non ideal solutions:

if the interactions (between solute and solvent) repel each other, the
activity coefficient is greater than 1.

How can interactions between molecules repel each other? Don't they always line up so that the negative end is in contact with positive (and vice versa)?


texts: When is there hybridization and when is there no hybridization? Do all structures have hybridization or only some specific structures have it and why?


texts: Can I use the quasi-equilibrium approximation when drug and ligand distribution volumes are different?

texts:
A drug $D$ binds a ligand $L$ to form a complex $C$ according to the law of mass action. Furthermore, mass balance should be achieved. Can I still assume quasi-equilibrium when the distribution volumes of the drug and the ligand are different?

From the quasi-equilibrium approximation it follows that

$$k_\mathrm{on} [D] [L]=k_\mathrm{off} [C],$$

from which the dissociation constant is

$$K_\mathrm{d} = \frac{[D][L]}{[C]} = \frac{\frac{D}{V_D}\frac{L}{V_L}}{\frac{C}{V_C}},$$

with $[x]$ describing the concentrations, $x$ the amounts, and $V_x$ the distribution volumes.

Mass balance now means that

\begin{align}
D_\mathrm{tot} &= D + C &
\text{and}&&
L_\mathrm{tot} &= L + C.
\end{align}

Can I now rewrite the equation for $K_\mathrm{d}$ as

$$K_\mathrm{d} = \frac{\frac{D_\mathrm{tot}-C}{V_D}\frac{L_\mathrm{tot}-C}{V_L}}{\frac{C}{V_C}} ?$$

Even though this might be very basic, I would really appreciate if someone could explain it in detail.


texts: How to calculate the mass of air that fits into a balloon of a certain size?

texts:
A hot air balloon has a $\pu{500 m^3}$ volume.
  How much mass of normal air fits into the balloon, if the relative molar mass is $\pu{28.8 g/mol}$?

I am not sure if I should simply use the $PV=nRT$ formula and therefore
$$1\times500= m/28.8 \times 273 \times 8.31 .$$

I feel that there is something wrong, can anyone enlighten me with the right formula or the basic concept of solving this kind of questions?


texts: How to find volume of substance from molar concentration

texts:
The concentration of a substance dissolved in water $i$ is known in (mol/m3), so is the molar mass in (g/mol) and the density in (g/m3).

I want to find the volume of this substance in m3.

I have two possible ideas for equations to use:
$$\mathrm{volume}_i= \frac{\mathrm{mass}_i}{c_i  \times M_{W,i}},$$
however, to use this equation I need to know the mass of the substance, which is not obvious.

Also I could use something like this:
$$\mathrm{volume}_i = \frac{c_i \times M_{W,i} \times \mathrm{volume}_{?}}{\rho_i },$$
however, I'm not sure what volume$_?$ would be, as I don't know the volume of the solution and I am trying to find the volume of the substance $i$.

Any ideas how to find the mass in the first equation or the volume in the second equation, or other equations to use?

Extra comments:
My real aim is to find the volume of the solution so I can use the following formula for volume concentration, where I already know the volume concentration $\phi_i $:
$$\phi_i = \frac{\mathrm{volume}_i} {\mathrm{volume}_\mathrm{solution}} $$
 or
$$\mathrm{volume}_\mathrm{solution} = \frac{\mathrm{volume}_i} {\phi_i} $$


texts: When exactly does the first drop of distillate appear in a distillation?

texts:
The below image (source: here) is from a fractional distillation of a mixture of two liquids, one with a boiling point of 69 degrees celsius and the other with a boiling point of 98 degrees celsius. In this diagram, it appears that the first drop of distillate occurs at the boiling point of the component with the lower component.

However, I was wondering why the first drop of distillate appears at the boiling point of the species with the lower boiling point, instead of being in between the boiling points of the two species.

My reasoning is here: If you start with a mixture of A and B, represented by point $a_1$, when you heat it, the first vapor will appear at point $a_2$ which corresponds to temperature $T_2$, which is in between the boiling points of either component.

Why does the first drop of distillate appear at a temperature equal to the boiling point of the lower boiling component, instead of in between the boiling points of the two components?


texts: Distinguish between symmetric and asymmetric molecules with IR

texts:
I get increasingly nervous as I get my organic lab course reports. For, I often get asked whether the peak in the IR comes from an asymmetric or symmetric stretch.

I've looked at about ten books and turned google upside down. But I still can't answer the question in every case, though our molecules are quite simple.

Can you help me out with a table or something equivalent?

The most urgent example is a $\ce{C-H}$ streching at $3006~ \mathrm{cm}^{-1}$ from p-tbutyl-(2-ethanol)-benzene (don't mind the nomenclature, please).


texts:
How did we derive the relation between the isoelectric pH and the dissociation constants for the amino and carboxyl groups on zwitterionic amino acids.

$$pI=\frac {pK_{a1}+pK_{a2}}{2}$$
where $$\ce{NH3^+-R2(COO^{-})<=>NH3^+-R2(COOH)-K_{a1}}$$
$$\ce{NH3^+-R2(COO^{-})<=>NH2-R2(COO^{-})-K_{a2}}$$

For more complicated cases (charged side groups) and their isoelectric pH, here is one site which just posts the equations without any derivation. Besides this, there is no reference I could find for this derivation.


texts: Amine group - electron donating or withdrawing group?

texts: Is the amine group a donating or withdrawing group? I think it depends on resonance. If the amine group can participate in resonance, the amine group is inductively donating. Resonance depictions below.


texts: What is the mechanism of synthesizing hydroxybenzotriazole?

texts:
I have big problem with this reaction.

Is this nucleophilic substitution? Cl is removed by hydrazine? It's my only idea, I don't know if this mechanism below is correct for this example:


texts: Heat energy of phosphoric acid evaporation

texts:
Looking at a system in which phosphoric acid is concentrated in an evaporator which uses a constant recycle stream with a heat exchanger in this stream to heat the acid so that water evaporates out of the acid when it re-enters the main stream, How can I find the Q needed to remove a certain amount of water from the stream in order to concentrate the acid to a specific level?

I am given the amount of water evaporated, both concentrations, and the flow rate of both the entering acid stream and the exiting acid stream. I have also been told that you cannot simply use $Q=mC_p\Delta T$, because this is inacurate for phosphoric acid.

Any help or sources you could link me to would be greatly appreciated.


texts: How can I mix methylene chloride, methanol and hydrofluric acid to make a paint stripper?

texts:
HF paint stripper on data sheets lists
Methylene chloride 70>85%
Methanol           10>25%
Hydrofluric acid.   5%
Previously I have found the chemical splits. Is there a particular method to properly blend all 3 parts?


texts: Do I understand correctly that simulation volume influences relative permittivity calculations? If so, how is the result useful?

texts:
I am having a lot of trouble understanding the influence of volume on relative permittivity/static dielectric constant.  I'm not a chemist, but am using molecular dynamics to calculate relative permittivity for use in other work.

A predecessor used this equation for relative permittivity $ε_\mathrm{r}$:

$$ε_\mathrm{r} = 1 + \frac{4π\sigma_M}{3k_\mathrm{B}TV}$$

where $V$ is the volume of the simulation, $T$ is temperature, $\sigma_M$ is the variance of the total dipole moment, and $k_\mathrm{B}$ is the Boltzmann constant.

Here is what I do not understand:  If I use a different $V $(i.e., a different number of atoms) for my simulation compared to my predecessor, then my calculated relative permittivity will be different from his.  I have done this to make sure, and indeed, the difference is quite significant.

Is there something silly I am misunderstanding here?  Like "$V$" is not the average box/cell volume of the simulation, but something that is not size-dependent?


texts: Reductive amination of (protected) 3-Oxopropanenitrile: Will azetidin-2-ol be formed via intramolecular ring closure?

texts:
What happens during this reductive amination?

I got the first product; the lithium aluminium hydride will reduce the nitrile to an amine. But what about the reductive animation step? As far as I can see the C=O will be protonated by the strong tosic acid, and then there will be a competition between the methanol and the internal amine to attack C=O. Actually, the amine is able to attack the C=O without the C=O being protonated, but still, this intramolecular seem too favorable given that we are forming a 4-membered ring. So will the methanol outcompete the amine? In that case what's up with the reductive animation step?

This is what I think happens after the second step ... I am going through the intramolecular route ... since that's the only way we get an iminium ion, on which the sodium cyanoborohydride can act.


texts: Recrystallization of salts with similar solubilites

texts: If you had two solutions, for example, 100 ml each of 0.5 M $\ce{RbCl}$ and 0.5 M $\ce{NaBr}$, at 20 °C, where the salts have very similar solubility in water, and you mixed the solutions, and allowed the water to evaporate. Would you theoretically end up with equal number of moles of $\ce{RbCl}$, $\ce{RbBr}$, $\ce{NaCl}$, $\ce{NaBr}$? If not, is there an equation or methodology you can use to determine how much of each salt you'd end up with?


texts: Why does NF3 have a smaller bond angle than NH3?

texts:
I've already read many answers about the reason why $\ce{NF3}$  has a smaller bond angle than $\ce{NH3}$ , but I can't seem to understand them. Here's my understanding of the situation:

$\ce{NH3}$: Here N is more electronegative than H so a large electron cloud is crowded over N. This will push the bond pairs $\ce{N-H}$ away from the central atom. So, the angle of $\ce{H-N-H}$ will decrease.
$\ce{NF3}$: Here F is more electronegative than N, so the lone pair cloud over N is scattered into the $\ce{N-F}$ bonds. Thus the smaller electron cloud over central atom is unable to push the $\ce{N-F}$ bonds away from itself as much as it did previously. So, bond angle should be higher than previous case.


texts: Oxidation number of oxygen atoms in oxygen difluoride

texts:
My textbook says:

Oxygen is assigned an oxidation number of $+1$ in oxygen difluoride. The number assigned to each Oxygen atom will depend upon the bonding state of oxygen but this number would now be a positive figure only.

Can there be multiple bonding states for oxygen in oxygen difluoride?
What can be the oxidation state of each oxygen atom in oxygen difluoride?


texts: Should I add more of a trihydrate chemical to a solution if recipe calls for hemihydrate?

texts:
I am running phosphate by the ascorbic acid method (SM 4500-PE, PDF), and making the antimony potassium tartrate reagent. Standard methods uses $\pu{1.3715 g}$ of $\ce{K(SbO)C4H4O6 * 1/2 H2O}$ per $\pu{500 mL}$, while the chemical I have is $\ce{C8H4K2O12Sb2 * 3 H2O}$.

Should I add proportionately more of the trihydrate chemical to make up for the weight of water? I'm not sure what the exact active ingredient here is, and I realize that there are different chemical formulas besides the water content. But, I am hoping that if I account for the difference in weight of water, then I will get at least closer to the appropriate amount of necessary active reagent.


texts: Rate-determining step of Claisen condensation

texts: If we use a strong base such as LDA or NaH, will the rate-determining step  change from enolate ion formation to nucleophillic acyl substitution step?


texts: Is there a substance that is hard (ideally abrasive) in solid form but would dissolve in water?

texts: doing some research for a dishwasher / dish cleaning product and interested in any compounds that could be fashioned into a brush or other abrasive form and then dissolve and wash away with the water cycle?


texts: Why does graphite have a high melting point even though its intermolecular forces are weak?

texts:
From what I've read online, when a substance undergoes a state change, the intermolecular forces are broken. The covalent bonds are not broken (http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/chemicals/airmolecularrev2.shtml)

My textbook states that layers of graphite can slide over one another easily and can break of one another as they have weak intermolecular forces.

I thought that if an object has weak intermolecular forces, its melting point is lower. Why does graphite have such a high melting point if its intermolecular forces are weak?

My textbook also states that the strong covalent bonds are broken during state changes, isn't this incorrect?


texts: Does the temperature during this reaction remain constant?

texts:
Considering all gases to be ideal, the enthapy change for the reaction
$$\ce{I2 (g) + H2 (g) -> 2 HI (g)}$$
is $\pu{−106.78 kJ}$ at $\pu{350 K}$.
To find the change in internal energy the formula we use is
$$\Delta H = \Delta U + (\Delta n)RT \, .$$

To derive this equation we must have assumed the temperature during the reaction to be constant in the expression
$$\Delta H = \Delta U + \Delta(nRT).$$
I know that $\Delta U$ depends on temperature and the amount of substance, but if we assumed the temperature to be constant then $\Delta U$ should be $0$,
as the amount of substances of reactants and products are also the same, but it has a non-zero value. Is this possible?


texts: Is the volume of a protein substrate equal before and after an enzymatic reaction? (pepsin degrading egg white suspension)

texts:
I am trying to determine the reaction rate of pepsin at different pH values by performing an experiment.

I am using egg-white suspension as the substrate and am adding differently concentrated $\ce{HCl}$ to the substrate to vary the pH of the reaction. Eventually, I add the enzyme. However, for the reaction rate I require the time and the substrate disappeared and product formed.

Is the volume of the egg-white suspension different before and after the enzymatic reaction so that I could use it to calculate the reaction rate or does the protein's volume remain the same after the reaction?


texts: Is there way to detect surface area of nanoparticle by electrochemical technique?

texts: I want to know other than SEM is there any other technique or instrument to detect the surface area of particle esp eletrochemical way.


texts: Temperature & time necessary to carbonize all organics

texts:
Suppose that I have a cast-iron pot which my awful roommate has vigorously scrubbed with soap and left to soak in soapy water over the weekend. The seasoning has been destroyed and replaced with awful-tasting soapy contaminants.

It seems to me that the simplest and best way to deal with this is to heat the pot over a campfire until only black carbon remains, then clean and reseason.

Not knowing exactly what is in my awful roommate's dish soap, and being a very fussy foodie, I want to be conservative here... so how hot would I have to heat the pot, and for how long, to be quite sure that virtually nothing but carbon remains?

Edit: Compare using the self-cleaning cycle of an oven for similar purpose, reported to work well...


texts: Does pure HCl (without water) is an acid?

texts:
Hydrochloric acid is always discussed as dissolved in water, and acidity is measured in terms of pH by the concentration of the hydronium ion.
Is pure HCl still an acid, and if so, how can we measure its acidity?


texts:
I've read in some book that one of the old chemists was able to transform cheap metals into gold.

I know that gold is an element (Au) so we can't transform a metal into Au. But as I read further it says that the chemist doesn't actually transform metals into gold but into something very similar to gold (similar physical and chemical characteristics )
such that you can't differentiate between it and between gold.

Is this chemically possible?


texts: Triiodide ion gravimetric analysis Reaction Equation

texts:
Last week I did a gravimetric analysis from the following reaction.

$\ce{AgNO3 + (CH3)4N+I3- -> AgI(s) + (CH3)4N+NO3- + I2}$

The objective was to identify if my reactant was triiodide or pentaiodide. In order to find out we reacted $\ce{AgNO3}$ in excess so all iodide ions precipitated and no $\ce{I2}$ was formed. Then, $\ce{AgI}$ could be weighted and calculations would tell you the valence of the ion.

Question is, if no $\ce{I2}$ is formed, you expect to have $\ce{3 AgI}$ precipitating. But how do you balance the equation?? This is the unbalanced equation:

$\ce{AgNO3 + (CH3)4N+I3- -> 3AgI(s) + (CH3)4N+NO3-}$

I don't need the answer, I am just curious because my professor could not solve the problem.

Thank you and good luck!


texts:
For the synthesis of $\ce{KMnF3}$ I said the reaction equation was

$\ce{3KF + MnCl2 -> KMnF3 + 2KCl}$

Is it this simple or are am I missing something with these particular types of reactions?


texts:
Am aware that one method for testing for the presence of $\ce{CO2}$ is passing the gas through limewater, with it going cloudy if positive.

Are there any other convenient methods?


texts: Information depth in x-ray photoelectron spectroscopy (XPS)

texts: What is 'information depth' in XPS and what does determine it? Also how does it depend on the 'take-off angle'?


texts: What are the mechanisms for the reduction of organic compounds employing red phosphorus and iodine?

texts:
I was recently studying oxidation and reduction reactions.

I found red phosphorus and iodine reduce many different organic compounds.

Out of interest I would like to know the mechanism for these reactions. A concerted path is preferred.


texts:
The conversion between different chemical structure formats, e.g. from .mol2 to .xyz, by openbabel may tied to conditions to be met.  One example of such a filter is to allow such a conversion only for data sharing a certain scaffold, e.g.

babel -imol2 AHECAS.mol2 -oxyz AHECAS.xyz -s "c1ccccc1-[#16](=[#8])-[#6]-c2ccccc2"

So the program allows SMARTS as constraining input parameter.  In difference to SMILES, (apparently, based on babel -L formats) openbabel however does not offer a conversion of any format into SMARTS and my source to generate them is the on-line PubChem Sketcher.

Question:  Aiming to generate SMARTS locally (offline), I know Marvin by ChemAxon may export a structure into SMARTS.  However, is there a portable alternative (with lesser footprint than a complete new GUI sketcher), preferentially allowing a conversion in a pattern like SMILES2SMARTS (or mol2toSMARTS) from the terminal / by a script?


texts:
[If you don't like to read the question just look at the 3 pictures the first one has the carbocation which have to be stabilised by ring expansions the other 2 are my predicted structure so please confirm which one is correct or if both are wrong please provide the correct one]

please help me in expandin the rings in the following structure :

I tried a lot expanding the the rings twice to get this :

but the intemediate in this structure is unstable as it has a bridge carbocation.
instead we can have a intermediate with sigma pi resonace stablising the carbocation by expanding the ring once as follow  :

I cant wrap my head which one is correct?


texts: Is Alkanol an official part of chemical Nomenclature?

texts: There are several references to alkanols here and here but neither of these sources are too reliable. The IUPAC gold book seems not to recognise the term and a quick google search reveals no really good sources.Whilst still not a super reliable source the fact there are no results on Wikipedia but simply a redirect to alcohol also furthers concerns and so the question is: Is the term Alkanol a 'real', 'proper', and 'official' term in chemistry?


texts: Precautions and tips for Qualitative Inorganic Analysis of Coins

texts:
I'm a highschool student and as part of an investigatory project, I have decided to analyse which metals are present in our everyday coins.

I chose this because in my previous academic year, I had learnt how to analyze the cations present in inorganic salts and I employed the same systematic analysis method that I had learnt to test the presence of metal cations in some coins.

Obviously, I cannot expect the coin analysis to go exactly like the salt analysis. I would have to ignore certain tests like the 'flame test'.

Could you please tell me what precaustions I should take for this experiment? I wish to write up a clear and systematic process by which any student / coin collector can easily do in a laboratory with only common chemicals and salts.

All advice, resources and tips will be most appreciated.


texts: Coconut oil vs Olive oil: Spray dynamics

texts:
Ps: If this would better fit Physics then please move it there or let me know. I put it here based on fact that viscosity and colloids were part of chemistry curriculum 10/15 yrs back in school.

Let's say we had to spray Edible oil.

How would spraying each differ?

How different are their Physical Properies when it comes to spraying and how would they affect the spray and compare with each other?

(You may point out Properies that matter in spraying that I may not be aware of, but these are few I can remember from school/ college such as viscosity, stickiness, cohesion, adhesion, density)

Also, I understand temperature would/ could play a role as well, so let's specify and put them at their ideal temperature for spraying.

Let's optimize this spraying experiment for both of them & compare.

I'd love to hear the science in play here.

Ps: I'm curious if any of the follow terms apply to these Virgin oils: homogenous, colloidal, plasma?


texts: Does burning graphite give off carbon monoxide?

texts: Put $\pu{3.7V}$ through a graphite rod, I know graphite doesn't burn but it did smoke. So I automatically assumed it to have gave off $\ce{CO}$, so I've aired out the house $\ce{CO}$ Detector, but it did not go off. I know they only detect above $\pu{30PPM}$, but does burning heating graphite rods give off $\ce{CO}$?


texts: Quantitative information from silica gel TLC plate?

texts:
I have a general question about thin-layer chromatography using silica gel.

Can we get quantitative information from a TLC analysis? Is this mainly just the Rf or can we tell more? I'm guessing purities, the number of compounds, and identity are qualitative aspects.


texts: Why is the current draw dropping in water electrolysis

texts: We've done an experiment regarding water electrolysis. Basically, we just separated the oxygen and hydrogen gas in a beaker that contains a magnesium sulfate solution. We set the power supply voltage to 12.46V with an initial .09A and final .01A over 45 mins. I was wondering as to what causes the drop in current draw. I have my suspicion that the concentration of the solution is decreased since we're using copper wires, and there was a displacement reaction between copper and magnesium sulfate.


texts: Andersen thermostat in MD with rigid bond constraints

texts:
I have been writing a custom MD code for some time. I have been using the Andersen thermostat, mainly because its ease of use, and the fact that I am not concerned with gathering dynamical data, but rather free energies. I have implemented the SHAKE algorithm found in LAMMPS. However, the thermostat seems to be undercooling now, when constraints are present. For instance, if I make the set point temperature 350 K, my system will equilibrate at around 330 K.

I am calculating the number of degrees of freedom for the temperature calculation as $3N-3-$number of bond constraints. Has anyone else had a similar experience with the Andersen thermostat? Would a Langevin thermostat work better here? Why is the Andersen thermostat not playing well with the SHAKE algorithm?


texts: Confidence in conformation search results from molecular mechanics

texts:
Conformational searches using molecular mechanics can be either systematic or 'random' using Monte Carlo methods (or other non-systematic methods) to sample conformational space.

In general, my understanding is that Monte Carlo methods perform just as well as systematic searches # assuming that the right parameters are used. This is often described in (organic) computational papers along the lines of :

  A sufficient number of conformations were explored such that all low-energy conformers within  a X kj/mol window of the global minima were found at least X times.

There is a lot of ambiguity over how many times a low energy conformer needs to be found in order to 'guarantee' that the conformational space has been fully explored. Certainly, in my own experience I can generate an ensemble that fulfils this criteria but is clearly non-complete (if I run the same search from a slightly different starting geometry I generate another ensemble with some different low-energy conformers).

My question is two-fold:

Is there any mathematical basis for the statement about finding a low energy conformation x times, or is it largely a case of convenience that works well empirically in the majority of situations ?
Is there really any way to know that a search is comprehensive without systematically exploring the entire PES ?

#: There was a report that Ken Houk lost a bet due to his belief that systematic sampling was the only true way to explore a potential energy surface, though I cant find the paper where this was discussed.


texts: how to separate a mixture of sodium chloride and sodium hydroxide

texts: I recently did an double displacement reaction in that I have formed a solution of water with sodium hydroxide and sodium chloride are dissolved in it. now I want to separate both of them


texts: Can I use potassium acetate instead of potassium carbonate?

texts: In the synthesis of N-ethoxycarbonyl L-proline methyl ester from L-proline and ethyl chloroformate, I use $\ce{K2CO3}$ to neutralize $\ce{HCl}$. Can I use $\ce{CH3CO2K}$ instead of $\ce{K2CO3}$? I think I cannot use it because it reacts with $\ce{HCl}$ forming acetic acid which can hydrolyse the ester. Is it correct?


texts: How do acids prevent ferrous sulfate from getting oxidised?

texts: If $\ce{FeSO4.7H2O}$ is dissolved in an acidic environment, for example in 0.05 M aqueous solutions of methanoic or ethanoic acid, would that prevent it from getting oxidized if an oxidizing agent like bromine water was added to it? If so, how? Since this is not examining oxidation with respect to air or oxygen.


texts:
In this chart, I can see that stable nuclides (other than hydrogen) have a neutron count greater than or equal to their proton count, and that the neutron:proton ratio for stable nuclides increases with atomic number.
I can also see that in many cases, radioactive nuclides which have excess neutrons undergo beta minus decay, converting one of the excess neutrons to a proton, and moving toward that stable ratio.
I can see why having excess protons might make an atom unstable: they have positive charge and push each other apart. But it seems to me that excess neutrons would make it more stable, adding to the strong force between the nucleons.
Why is an atom with excess neutrons unstable?


texts: A gram of salt added to pure (distilled) water introduces around $2 \times 10^{22}$ ions?

texts:
I am currently studying Practical Electronics For Inventors, Fourth Edition, by Scherz and Monk. Chapter 2.5.2 Resistivity and Conductivity, claims the following:

  Adding an ionic compound in the form of common salt ($\ce{NaCl}$) to water increases the ion concentration within solution -- $\ce{NaCl}$ ionizes into $\ce{Na^+}$ and $\ce{Cl^-}$. A gram of salt added introduces around $2 \times 10^{22}$ ions. These ions act as charge carriers, which in turn effectively lowers the solution's resistance to below an ohm per meter. If we use the solution as a conductor between a battery and a lamp -- via electrodes placed in solution -- there is ample current to light the lamp.

How did the authors calculate that a gram of salt added introduces around $2 \times 10^{22}$ ions?

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