texts: If I have a solid and want to make an aqueous solution of 70%, how much water do I need? Is it as simple as weighing out 70 $\mathrm{g}$ of solid and adding water until I have 100 $\mathrm{mL}$? Will this solution be 70 wt. % $\ce{H2O}$?


texts: Are multiple transition states possible? Criteria to choose the correct one?

texts:
I am studying a reaction using electronic structure methods using various software packages (ORCA,GAMESS, G09) and have found two possible transition structures between product and reactant. Both have imaginary frequencies, but each has a different energy value, frequencies and geometries. Some software coincide in the found transition state while other differs, adding to the confusion.
So my questions are:

Is it possible to have multiple transition states, if so what is a good criteria to choose between candidate states?
Should I expect the frequency to be within certain range? (for example if the reaction is the movement of a H atom within the molecule)
Is there some quantitative value(s) (energy, vibration amplitude/frequency, vibration 3d direction vectors, 3d geometry, etc.) that can be used as a reasonable measure to choose the "correct" state? (That is to avoid visualizing the imaginary mode of vibration or computing the IRC).


texts: What is the colour of chromium(III) chloride solution?

texts: I had a question asking about the colour of the solution of chromium(III) chloride in my exam, all my colleagues have different answers, I couldn't find any exact answer after searching!


texts: Dibenzoyl-L-tartaric acid won't show up on HPLC chromatogram

texts:
I'm trying to develop a method for HPLC to detect dibenzoyl-L-tartaric acid. Concentration doesn't matter at this point; I'm only concerned with detection. The problem I'm having is the compound won't show up at any wavelength I've tried. I think I have the appropriate column (one specifically designed for organic acids). The run time is more than enough, the sample is essentially saturated and my injection volume is 25 mL.

The compound seems like it would have a chromophore, so I've been trying wavelengths between 210 and 270, but nothing works. Literature also turns up nothing.

Can anyone steer me in the right direction?


texts: If concentration of K+ ions inside the cell is almost equal to concentration of Na+ ions outside of the cell why these ions cross the membrane?

texts: I'm a bit confused about electrochemical gradients of sodium and potassium ions. They have similar concentrations and are kind of similar ions but their distribution is different across the membrane. If that is true why they cross membrane. Why don't these gradients somehow cancel out? Why is there even need for sodium to enter the cytosol when potassium ions which are also positive are already inside?


texts: Why does Le Chatelier's principle not apply to pure solids and liquids?

texts:
If we had a homogeneous reaction of pure liquids only, would Le Chatelier's principle still apply ?

Also, wouldn't increasing the amount of solid in a heterogeneous reaction mixture at equillibrium result in more product, therefore indicating a shift in equilibrium?


texts: ∆S (Entropy change) is given by ∆H/T (∆H = Enthalpy change , T= absolute temperature). Then how can the Entropy change for a reaction be negative if the Enthalpy change is positive, and vice versa?


texts: Which chemicals could be used to dissolve Polybutylene Terephthalate (PBT), but not dissolve brass?

texts:
This is for a recycling project, I am looking to recover brass pins from electronic connectors made of glass reinforced Polybutylene Terephthalate (PBT).

The objective is to find a chemical which would be able to dissolve Polybutylene Terephthalate (or PBT, a common type of plastic) so that i can separate the brass pieces inside, without dissolving them too. I think that if it dissolves PBT the glass reinforcement will become dust so it won't be an issue.

So far my search has been unsuccessful, either it was acids which were too strong and would also dissolved] the brass, or common solvent which had no effect on the PBT (tested Acetone). Even 30% Caustic soda doesn't attack the PBT.

I found a method with high temperature methanol under pressure into a closed stainless steel shape, but it's way too complex for me to make. Similarly chemicals which are too cancerogenous are not worth it (at least given that i am not a specialist capable of handling the most dangerous ones).

If anyone has an answer or some ideas i'd love to hear it!

Thanks a lot!


texts: Can silica gel beads cause silicosis if crushed?

texts: Can silica gel beads (which I believe are amorphous) when crushed to dust cause silicosis?


texts: Why does increasing availability of microstates compensate for increased energy of products in an endothermic spontaneous reaction?

texts:
I'm wrestling with the idea right now of processes that are both endothermic and spontaneous.I understand that there must have been an associated increase in entropy.
How does an increase in "microstates" compensate for the fact that a chemical reactions products have overall "more energy" than the reagants?
Edits: Clarified question
My attempt: Two closets have same volume, except one has shelving and the other doesn't. The closet with shelving is "preferred" because it is able to "handle" more shoes ("energy") than other closet because there are more ways to arrange those shoes (on the shelves).  The shelved closet with 10 shoes is more "organized" than the nonshelved one with 8 shoes. Which means, in my analogy, Gibbs is a measure of energy "organization."


texts: How to determine the shape of hybridized atomic orbitals in VB theory?

texts:
From diagrams, it's rather obvious how $sp$ orbitals are hybridized - the hybrids are just a composite of the $s$ and the $\pm p_{(x)}$ orbitals. However, $sp^2$ orbitals are not just composites of $s, \pm p_x, \pm p_y$, and the same goes for $sp^3$.
This incongruity leads to my question.
I am aware that the general shapes are trigonal planar and pyramidal, respectively. However, I recall learning of a more mathematical approach that used the wave function (I think?)
In my notes, I found this formula.
$$\Phi_i=\sum_{j=1}^nc_{ij}\phi_j, i=1,2,3...n$$
My understanding is that $n$ is the number of atomic orbitals (and thus also the number of orbitals). I believe $c$ is a constant, and $\phi$ is the orbital.
Later, for $sp^2,$ I have the following formulas:
\begin{align}
\require{cancel}
\Phi_1 &=c_{1,1}\cdot s+ \cancelto{0}{c_{1,2}\cdot p_x} + c_{1,3} \cdot p_y &&= c_{1,1}\cdot s+c_{1,3} \cdot p_y\\
\Phi_2 &=c_{2,1}\cdot s+ c_{2,2}\cdot p_x + c_{2,3} \cdot p_y &&= c_{2,1}\cdot s+ c_{2,2}\cdot p_x + c_{2,3} \cdot -p_y\\
\Phi_2 &=c_{3,1}\cdot s+ c_{3,2}\cdot p_x + c_{3,3} \cdot p_y &&= c_{3,1}\cdot s+ c_{3,2}\cdot -p_x + c_{3,3} \cdot -p_y \\
\end{align}
I have some recollection that the wave functions zeroes out for particular quantum number values, but I can't remember how it all fits together with this equation.
I couldn't find this formula online, so I'm hoping that it might make sense to someone here.
Thanks for the help!


texts:
Simple question with a complex answer, certainly:

Why do some oils feel "dry," while others feel "oily"? Is the feel directly related to C-chain length, or hydrogenation, active groups, or something else entirely?

Thanks!


texts: How to compare volatility of inorganic acids

texts:
Extending This question further

Sulfuric acid because of its low volatility can be used to manufacture more volatile acids from their corresponding salts

To use this statement in practice I need to compare the volatility of the acids. My book states that using this principle above $\ce{HF, HCl, HNO3}$ can be formed as some examples.
I wish to ask how can I compare the volatility of inorganic acid without being provided the data. Is there any reliable method to do so? I see sometimes hydrogen bonding being used for this purpose but are there any more methods which cover a wider range of molecules ?


texts: Breaking/reducing water adhesion with an electric field

texts: Does anyone know if the presence of an electric field can help to reduce water adhesion to a surface?


texts: Balancing the redox disproportionation of chlorine by half-reactions

texts:
I am having some difficulty balancing the following reaction using the half-reaction method:

$$\ce{Cl2(g) -> Cl-(aq) + ClO3-(aq)}$$

My attempt at the problem:

By determining oxidation numbers it is possible to see what is being oxidised and what is being reduced:

$$\ce{\overset{0}{Cl}_2(g) -> \overset{-1}{Cl}^-(aq) + \overset{+5}{Cl}\overset{-2}{O}_3^-(aq)}$$

From this I determined the following two half-reactions:

Reduction Half: $\ce{Cl2(g) + 2 e- -> 2 Cl-(aq)}$

Oxidation Half: $\ce{Cl2(g) + 3 H2O (l) -> 2 ClO3-(aq) + 6 H+ + 4 e-}$

Net ionic equation: $\ce{6 Cl2(g) + 6 H2O(l) -> 8 Cl-(aq) + 4 ClO3-(aq) + 12 H+}$

The answer to this problem is however given as

  $$\ce{2 Cl2(g) + 6 H2O(l) -> 2 ClO3-(aq) + 12 H+ + 10 Cl-(aq)}$$

I have tried this problem several times over and cannot work out how this answer was reached.

Update:

Silly mistake, oxidation reaction should be: $\ce{Cl2 + 6H2O -> 2 ClO3- + 12 H+ + 10 e-}$ hence solving the mystery of why my answer is wrong.


texts: Proof for second-order perturbation term of energy

texts:
In perturbation theory, if
\begin{align}{\hat {H}} &= {\hat {H}^{(0)}} +  λ{\hat {H}^{(1)}} \tag{1}\\
{ψ} &= {ψ^{(0)}} +  λ{ψ^{(1)}} +λ^2{ψ^{(2)}} + ... \tag{2}\\
{E} &= {E^{(0)}} +  λ{E^{(1)}} +λ^2{E^{(2)}} + ... \tag{3}\\
\end{align}
then, by applying these three equations on ground state $ψ_0$ and using the general time-independent ${\hat {H}{ψ} = Eψ}$ , it can be shown that:[1]
$$E_0^{(2)} = \sum_{n \neq 0}\frac{|H_{n0}|^2}{E_{0}^{{(0)}}-E_n^{(0)}} \tag{4}$$
The proof can be found in quoted reference; it is too long and not shown here. There is one step reads:

\begin{align}\int{ψ^{(0)*}_0}&\hat {H}^{(0)}{ψ^{(2)}_0} dτ + \int{ψ^{(0)*}_0}\hat {H}^{(1)}{ψ^{(1)}_0} dτ = \\ &E^{(2)}_0\int{ψ^{(0)*}_0}{ψ^{(0)}_0} dτ + E^{(1)}_0\int{ψ^{(0)*}_0}{ψ^{(1)}_0} dτ + E^{(0)}_0\int{ψ^{(0)*}_0}{ψ^{(2)}_0} dτ\tag{5}\end{align}
the first and last terms cancel.

I don't see why the first term (on LHS) is equal to the last term (on RHS). Based on the first three equations above, we can only conclude
$$\hat {H}^{(0)}{ψ^{(0)}_0} = {E}^{(0)}_0{ψ^{(0)}_0} \tag{6}$$
Why is $\hat {H}^{(0)}{ψ^{(2)}_0} = {E}^{(0)}_0{ψ^{(2)}_0} $? Also, why is ${ψ^{(2)}_0}$ also an eigenfunction of $\hat {H}^{(0)}$, with same eigenvalue as that of ${ψ^{(0)}_0}$? I believe it has something to do with linearity of quantum mechanics, but not able to prove it.

Reference
[1]: Peter Atkins, Julio de Paula. Physical Chemistry (8th Edition). OUP. 2006. Page 314-315.


texts: Exothermic reaction between sodium carbonate and castile soap

texts:
The other day, I tried to mix liquid castile soap and washing soda (sodium carbonate) to use in doing laundry. I mixed equal parts liquid soap and sodium carbonate by weight. To my surprise, an exothermic reation occured (my glass jar got warm), and then the substance became hard. Before it got hard, I touched the tip of my finger to it and didn't get any chemical burns.

The castile soap that I used was homemade. My soap contained: water, potassium soybeanate, and glycerin.

The soap was made of:
water 172.36g
potassium hydroxide 91.45g
soybean oil 453.59g

for a total of 717.41g before boiling down which I then dilluted to a water to soap ratio of 4:1. The soap was well cooked (5-6hrs) and cured for a week.

Could a chemist help me understand what reaction occurred?


texts:
I am trying the hypothetical synthesis below, but I didn't get the product I was expecting. Instead, the reaction formed mostly styrene, in >80% yield (elimination product of the bromide)

The synthesis of an analogous product with one less carbon in the bromide (benzylic bromide) is described in the literature and I thought it would work with this one since they only differ by a carbon. Any thoughts on how I could overcome this selectivity problem?

I thought about using a milder base, but I don't think the problem here is actually the base I use, cause they will all form the enolate, the problem is the enolate abstracting the benzylic proton from the bromide and generating styrene + butyrolactone.


texts: Why tungsten does not have stable configuration?

texts:
Whenever there are 4 unpaired electrons in d-orbital, elements try to attain stable electronic configuration. For example copper.

Electronic configuration of copper should be [Ar]3d4 4s2, but it tries to attain stable state and so it changes to [Ar]3d5 4s1.

I have seen it happens with most of the elements but not with tungsten. Electronic configuration of tungsten is [Xe]4f14 5d4  6s2 and not [Xe]4f14 5d5  6s1(more stable).

What is the reason behind that?


texts: Expression of the potential in the hydrogen atom while solving radial part of the wave function

texts:
I was reading about the derivation of wavefunction of Hydrogen atom from Atkins book. After the separation of variables and writing the  wave function, $\psi_{(r,\theta,\phi)}=R_{(r)}Y_{(\theta,\phi)}$, and further solving the equation, they reach the expression of potential as

$V_{eff}=-\frac{Ze^2}{4\pi\epsilon_0r}+\frac{l(l+1)\hbar^2}{2\mu r^2}$

The first term $(-\frac{Ze^2}{4\pi\epsilon_0r})$ represent the electrostatic potential between the electron and the proton. I am not able to understand the interpretation of the second term $(\frac{l(l+1)\hbar^2}{2\mu r^2})$. In book it is written that it arises from centrifugal effect.
Also why the second term is considered in the potential as potential is defined for a conservative force field? I know that second term in potential comes in picture as a result of the derivation. But the second term doesn't make sense to me as in Bohr's model,  in the expression of the potential we only consider the electrostatic potential. Please explain about the second term in potential.


texts: what makes an acid a strong acid or weak acid?

texts: When my teacher referenced nitric acid as a strong acid, I thought it was strong because it donates more than one H+ per molecule, but then I saw the equation is $\ce{HNO_3}$ and it only donates one. Acetic acid is also monoprotic, but it is considered a weak acid. What makes an acid strong or weak? If an acid donates more than one proton, does it make it stronger? Feel free to make any formatting changes to formulas as well.


texts: I have a question about the selectivity of m-CPBA in this reaction. In my experience, I have used m-CPBA for epoxidation of alkenes. It surprised me that in this reaction, the ketone reacts to give an ester and the alkene remains unchanged? Is it due to the presence of the overhanging ether group? Does this provide a sort of steric crowding so that the peroxyacid can't get in? Cheers.


texts: If the hydroxide ion is such a poor leaving group then why does water dissociate?

texts: Water dissociates into the hydroxide and hydronium ions but, why does this happen if the hydroxide ion is such a poor leaving group. Alcohols don't undergo $\ce{S_{N}1}$ reactions because the hydroxide ion doesn't dissociate so why does it happen in water?


texts: Does anyone know of a good example of two liquids mixing very exothermically? As a reference, I'm thinking more like NaOH and water boiling when mixed at room temperature than ethanol and water are exothermic but you'll never notice making a gin and tonic.


texts: Why super glue does not stick inside their own bottle?

texts: We usually use super glue to stick any two objects but I was wondering like why don't they stick inside their own bottle ?


texts: Analytical Chemistry predicting the order of elution of compounds in a reverse phase HPLC

texts:
Predict the order of elution for a mixture containing caffeine and benzoic acid, using a reverse phase HPLC. Explain your answer.

My try:

Since benzoic acid is more acidic that caffeine, which means it has a lower pH, it is hence more polar. Since for HPLC, the mobile phase is the polar phase, elution of polar compounds will be favoured hence benzoic acid will be eluted first. Is my answer and explanation correct?


texts: Why there is a non-linear trend on the melting points for period 2 elements, especially Na to Si?

texts:
Using the knowledge of periodicity from high school cannot explain this, what it tells me is just metallic bonding.

The model of delocalised electron from a metallic lattice can explain the increase of melting point from Na to Si, but it fails to explain why the relationship is non-linear?


texts: Defining equilibrium position vs equilbrium constant

texts:
My chemistry textbook says that $K_{p}$ indicates the equilibrium position. It then says that $kp$ will not change if pressure is increased, but it also says that the position of equilibrium does change if pressure is increased.

Let me restate that: $K_{p}$ tells you the equilibrium position. Increasing pressure does not change $K_p$ (indicating the equilibrium position does not change) but does change the equilibrium position. This is clearly a contradiction, so how should I properly define equilibrium position and equilibrium constants? I've never really had a clear understanding of what equilibrium position means.


texts: The negative absorbance values in the baseline measurement

texts: In the spectrophotometric analysis(uv-vis-NIR) of ITO Nanoparticles in tetrachloroethane using a double beam instrument baseline was measured with 2 identical cuvette with solvent only. This gives me only negative values for absorbance. Does this mean there is significant difference in transmission between the blank and the reference even if they are the same compound?


texts: How to increase the concentration of HCl

texts:
Today I have purchased some $\ce{HCl(aq)}$ on my local market with a concentration of 23%.
However, I need to obtain a concentration of 37% in order to perform an experiment. Can I use distillation process to increase the acid concentration?
If yes, can I use standard chemistry glassware to process it? (In an isolated system to prevent the $\ce{HCl(g)}$ from escaping of course.)

Distillation unit


texts: Would an explosion of an electrically charged material be more powerful than if it were not charged?

texts:
I was recently reading a book titled "Hitler's Suppressed and Still Secret Weapons, Science and Technology". I came across this book because I saw it referenced by someone on another site. The book's author claims that there is a variation of the typical fuel-air bomb (Where a cloud of explosive material is dispersed into the atmosphere and then detonated), whereby an explosive material is dispersed into the atmosphere, charged with electricity as much as possible, and then detonated. Supposedly, the explosion of this modified fuel-air bomb is more powerful than a conventional FA bomb. Alternatively, the explosive material is wrapped in an insulator and then charged. Now, I am very, very skeptical of this, especially since that book has been criticized as being into conspiracy theory territory. However, I am curious: If a material that acts as fuel were to be electrically charged (Like having a build up of static electricity) before reacting with oxygen, would it result in a greater release of energy than if it were not to be charged?

For instance, suppose that a cloud of coal dust happened to have a significant buildup of static electricity, and then it explodes. Would the explosion be more powerful than if the cloud did not have any static buildup?


texts:
Carbonyl has two resonance structures, where the $\pi$-bond between C and O breaks and the electrons "move" to the oxygen atom. This gives an empty p-orbital in carbon and a p-orbital in oxygen with two electrons, leading to a positive charge on carbon, and a negative charge on oxygen. To my understanding, oxygen gets the lone electron pair because it has a higher electronegativity than oxygen.

My question: is it possible that the two electrons "move" to carbon instead of oxygen, leading to a third resonance structure (I know that these resonance structures don't really exist, and that the real structure is somewhere in between), so that carbon has a lone electron pair? It would probably contribute little to the resonance energy compared to the other structures. Or is it not possible at all?


texts: How do I approach drawing all of the possible constitutional isomers?

texts:
Does anyone have any tips on how to approach these types of questions?
A specific example would be:

  Draw all constitutional isomers of $\ce{C2H4O}$

I can get the easier ones like vinyl alcohol, but it's hard to get ethylene oxide and it takes a long time for me to get acetaldehdye. And how would I know if I got all of the possible constitutional isomers?


texts: Why was anhydrous magnesium carbonate “upsalite” discovered so late?

texts: What complicated the synthesis of upsalite (anhydrous $\ce{MgCO3}$), for it to be synthesized and published in 2013 as opposed to the 20th century, as one would expect for such a simple salt?


texts: An ionic compound dissociates into 3 ions of 3 different elements?

texts:
When an ionic compound dissolves in water and becomes ions.

1) Typically we see:

$\ce{AB ->}$ Ions $\ce{A+ + B-}$

$\ce{ABC ->}$ Ions $\ce{AB+ + C-}$

2) But how about the one below, is there any case that will fit the situation

$\ce{ABC2 -> A+ + B+ + 2C-}$

or $\ce{AB2C-> A+ + 2B+ + C^3-}$


texts: Understanding how to calculate the pH of a buffer with ice tables

texts:
Let's say you are asked to calculate the pH of a solution with:

$\mathrm{0.1~M}~\ce{HCl}$
$\mathrm{0.2~M}~\ce{CH3COOH}$.
$K_\mathrm a = 2\times 10^{-5}$

This is how I would do it:

$$\ce{CH3COOH + H2O <=> H3O + CH3COO-}$$

The corresponding ICE table:
\begin{array}{|c|cccc|}\hline ~ & \ce{CH_3COOH}& \ce{H_2O}& \ce{H_3O^+}& \ce{CH_3COO^-}\\ \hline  \mathrm I & 0.2 & & & 0.1\\\Delta  & -x & & x & x\\ \mathrm E& 0.2-x & & x & 0.1 +x\\\hline\end{array}

calculate the pH:

$$\begin{align}
 K_\mathrm a &= \frac{\ce{[H3O+][CH3COO^{-}]}}{[\ce{CH3COOH}]}\\
  &= \frac{x \cdot (0.1+ x)}{(0.2-x)}
\end{align}$$
as $x$ is very small, we leave it out:
$$\begin{align}
 \implies 2\times 10^{-5} &= \frac{0.1x}{0.2}\\
 \implies 2\times 10^{-5} &= \frac{0.1x}{0.2}\\
\implies~~~~~~~~~~~~ x &= 4\times 10^{-5}\\ \implies
 -\log(x) &= 4.40~= \mathrm{pH}\\
\end{align}$$

First of all. Is this correct?
Where do you include $\ce{HCl}$? I didn't write it anywhere. And I see most of the people not writing the second molecule. How/where is it included?
What is the molecule in the first column of the ice table? What does it represent? Do you always write the acid in that column?

I made that exercise up. The original exercise has $0.1$ molar $\ce{HCl}$ and $0.1$ molar $\ce{CH3COOH}$. I changed it in order to clearly see which value is which one at which place in stead of all having the same ones. This is the original exercise:

\begin{array}{|c|ccc|}\hline & \ce{CH_3COOH} & \ce{H_3O^+} & \ce{CH_3COO^-}\\ \hline \mathrm I & 0.1 & & 0.1\\ \Delta& -x & x & x\\ \mathrm E &0.1-x & x & 0.1 +x\\ \hline\end{array}

\begin{align}K_\mathrm a &= \frac{x\cdot (0.1 +x)}{(0.1-x)}\\ &\approx \frac{x\cdot 0.1}{0.1}\\ \implies x&= 2\times 10^{-5}\\\therefore -\log(x) &= 4.70\;.  \end{align}


texts: How to dissolve the build-up from a paraffin based oil?

texts: I have a CNC lathes that use "oil" for cutting fluid during the machining of mostly metal materials.  Typically a heavy paraffinic based cutting oil (petroleum distillate) is used during machining.  My company switched suppliers of this cutting fluid and went to another cutting oil, supposedly with compatible chemistry.  This happened months ago.  Within weeks of making the switch the oil (the two oils mixed together) became slightly "sticky" or tacky.  This negatively affected the machine tools and processes and the decision was quickly made to go back to the original product from the original supplier.  Over a period of several months the reaction between the two products has left a byproduct of build-up of some type inside the machine tools.  I'm thinking it's the paraffin separating from the oil (somewhat) and along with other components of the chemical make-up that's left this brown, sort of sticky, almost "glue-like" material all over the internal surfaces of the machines.  I'm looking for some solvent(s) that will quickly dissolve this material.  Acetone seems to work but by itself it's not a great option.  The fumes are a problem, it evaporates too quickly.  Any other ideas?


texts: How does fat affect the precipitation of proteins?

texts:
I am doing an experiment using milk, heavy cream, and vinegar. We are trying to precipitate proteins from milk and heavy cream.

When I did the experiment with milk, it was very quick reaction and easily to isolate the casein polymers with vinegar added to the heated milk. This does not occur when the same process is used with heavy cream. I have tried to find out how this process fails with the heavy cream online and in my book there is a decent portion of the chapter dedicated to fats, but it doesn't mention why polymer creation can not occur in this experiment.

Can some one please help me with the reason the heavy cream doesn't curdle?


texts: How many structural isomers does 1,2-dimethyl-cyclohexane have?

texts:
Can someone tell me how many structural isomers exist for 1,2-dimethyl cyclohexane? My teacher said there is one structural isomer but I believe there aren't any because there is no other way to define the structure of the above compound such that they have the same molecular formula but a different structural formula. Also, we need two or more compounds to define isomerism, so how can a single molecule be ever defined as an isomer if there isn't any other compound to compare it with?
Also can structural isomers be defined if the position of substituents is already defined as in the case of above compound where the positions of the two methyl groups are defined beforehand (i.e. 1, 2)?


texts: How metal-plating on plastics is performed?

texts:
Metal coated plastics are commercially abundant now-a-days. I want to know how they're plated.

Before posting, I did a quick search and found a nice link. It refers to this process as metallization, although I'm not convinced by the term. Is it right ?

That site already provided the basic information. However, it would be great if someone can mention a few examples(which metal/plastic used) for the various methods deployed.


texts:
I have tried 4 experiments at various temperatures to melt obsidian.
At varying temperatures it just bubbles up and I don't seem to reach a melting point.

Do you know what gases obsidian might contain and would they be the cause of the bubbles?


texts: Relationship between heat and standard enthalpy for a reversible reaction

texts:
The enthalpy change for a reaction is equal to the heat absorbed at a constant pressure.

My notes say that the standard enthalpy change is the heat absorbed when the reactants (in their standard states) are completely converted to products (in their standard states). It uses this as an explanation as to why it is only possible to use heat measurements to determine  the standard enthalpy of reaction for a reaction that goes to completion.

I am not sure why it is the case that the reaction must go to completion for heat flow to be equal to the standard enthalpy change.


texts: Solvents for tartrates / tannins that won't attack glass

texts:
At the bottom of my wine decanter (which due to its shape is fantastically hard to clean mechanically) a layer of reddish brown precipitate forms. I believe this is probably potassium bitartrate crystals, which are coloured reddish brown by the presence of tannins, which in essence is a polyphenol.

I would like to know whether there is a chemical that I could use to clean the decanter with minimum mechanical action. I have tried water (with and without soap), alcohol (in the form of vodka), isopropanol without success. I have yet to try acetone. Preferably the solvent should not be greatly toxic (at least I'd like to be able to wash it out with water and reuse the decanter), and not react with high lead-content glass (which is what decanters are made out of) - hydrofluoric acid is thus to be avoided (as usual). It is unsurprising alcohol doesn't work as the reason tartrates precipitate is apparently because they are not soluble in alcohol. It would also be useful if I could purchase the solvent outside a lab environment.

My understanding is that potassium bitartrate is more soluble in acid solutions. I've tried citric acid (made up from powder) and vinegar, but the effect if any is modest.

I don't much care if the method used is to react with (rather than dissolve) the precipitate.

(Note this question is in part a thought experiment. I realise that in fact the best way to clean decanters is generally mechanical despite the difficulties, and I'm familiar with the copper beads method and the egg-shell method, as well as no end of sponges on bendy sticks. However, I'd like to know whether there is a chemical way. Also note that I added an 'equipment' tag as it's possible that some know-how from cleaning chemistry glassware might be useful here)


texts: Which chemicals can counter the corrosion of tamperproof hardware encryption chips?

texts:
I'm moving from software implementations to hardware. I need to reverse engineer silicon chips, though the tech that I want to study may have a corrosive chemicals that's supposed to destroy the chip upon touching.

What chemical gets sprayed onto the hardware and which chemical reactions occur?

If there's one substance that causes destruction then there must also be one that prevents it. Does anyone know what this chemical is?

This question in currently going on in the back of my head. Chemistry isn't really my thing; but I know enough to understand the chemical reactions to make various drugs.

I'm not funded by government. This is independent research. The field of cryptography is somewhat of a front line of engineering. If there are no answers to the main question, chemistry resources in the context of silicon and the relating chemicals used in production as well as the securing in the post production will be accepted as the answer.


texts: Why does barium sulphate not dissolve in HCl while barium sulphite does?

texts:
Intuition tells me that the ionic bond in the sulphate must be stronger than that in the sulphite.
Is this true?
If it is then why? The charge on the barium ion is 2+ in both cases and the charge on the sulphate and sulphite ions are both 2-.
The sulphate has an extra oxygen atom. It's presence is somehow making the ionic bond stronger. But how/why?


texts: What does *oxidizing* have to do with *hydrogen*?

texts:
An oxidizing acid is a Brønsted acid that is a strong oxidizing
agent. All Brønsted acids can act as oxidizing agents, because the
acidic proton can be reduced to hydrogen gas.

(source: Wikipedia)
But what does oxidizing have to do with hydrogen? Isn't it about oxygen?
Like how iron becomes iron oxide after prolonged exposure to oxygen in the atmosphere?
So why is hydrogen relevant?


texts: To be very specific I'm looking at a supplement that contains 2,000 mg of magnesium glycinate. In that serving it sates there is 2oo mg of elemental magnesium. How much glycine is there?


texts:
When a word has to be split broken into multiple lines, it is almost always hyphenated. Chemical names can be considered words, or at least they consist of words. So the hyphenation should apply to them as well. However, hyphens often are integral parts of systematic chemical names. Therefore confusion might arise, whether such a hyphen emerged from hyphenation or if it is "mandatory". Are there any official rules for the (possible) hyphenation of the chemical names? I could not find any, yet. I am sure some journals could have it mentioned in their style manuals, but I am primarily interested whether this topic is mentioned by IUPAC.

In fact, I am undecided whether to represent inserted optional breaks in long chemical names (that have to fit into some fixed-width infobox) HTML(5) representation as &shy; or <wbr>, which however means hyphenation, and non-hyphenation, respectively.


texts: How does changing volume affect concentration of solutions?

texts:
My teacher performed an experiment and made us watch.

He prepared 3 conical flask containing 50 mL mixture of sodium thiosulphate, potassium iodide and acetic acid.
He also had 3 measuring cylinders containing 12.5 mL, 25 mL and 50 mL of hydrogen peroxide of the same concentration.
He added few drops of universal indicator to each of the flask. Then he added the $\ce{H2O2}$ to them as well and started timing.

The general idea is that the indicator is going to change colour from orange to green, which is the colour when he stopped timing. The flask added with 50 mL $\ce{H2O2}$ had the shortest time recorded.

It is intuitive that higher volume of $\ce{H2O2}$ added will increase the speed of reaction but I don't know how to explain it. In kinetics we learn the effect of concentration on rate of reaction, but i cannot use this idea to explain because the concentration does not change! All three solutions of $\ce{H2O2}$ added has the same concentration because they are undiluted (He did not add distilled water to the $\ce{H2O2}$ solutions to make them the same volume).

So how can I explain why the use of higher volume (50 mL) will make the reaction go faster?

An example of the experiment can be viewed through youtube :
https://www.youtube.com/watch?v=Tlj5RvCSpLw


texts: Formal charge of oxygen in protonated alcohol

texts:
When ethanol is attacked by positive hydrogen ion, how can the oxygen atom acquire formal positive charge?
I tried calculation it as : $\frac{6-4}{2-1}$ which gives answer 3, but the answer should be 1. Can someone explain this?


texts: Plotting the data using Beer-Lambert law

texts:
For the spectroscopy lab we had a stock dye ($\pu{1.00E-4 M}$ Erioglaucine Blue) that we had to dilute. We had to dilute $\pu{1 mL},$ $\pu{3 mL},$ $\pu{5 mL},$ $\pu{8 mL},$ and $\pu{10 mL}$ in $\pu{100 mL}$ of water and measure their absorbance $A.$ I obtained the following data:
$$
\begin{array}{ccc}
\hline
V/\pu{mL} & A & λ/\pu{nm} \\
\hline
1 & 0.127 & 629.0 \\
3 & 0.342 & 626.2 \\
5 & 0.550 & 627.6 \\
8 & 0.850 & 628.3 \\
10 & 1.064 & 626.9 \\
\hline
\end{array}$$
How do I get the concentration in $\pu{mol L^-1}$ in order to make the graph? If I could get one example from this data set I should be able to calculate the rest for myself. I just need a head start.


texts: Fat polymerization vs hydrolysis and temperature change

texts: I have an experiment on fats that I have to do in a few hours and I am very lost between fat/oil (lipid) polymerization due to high temperatures and hydrolysis. It appears that both result in the breakdown of fats but in very different ways. Our class assistant suggested to do an experiment about different temperatures affect fat breakdown which results in acid creation that affects pH. I would track that ph change at different temperatures with different fats for the experiment. Please help as I am lost if that can even be done with simply a heating system, different fats and oils and pH strips??


texts: Why is 1-bromo-3-methylbut-2-ene named like that and not as 2-(bromomethyl)but-2-ene?

texts:
I had this confusion related to nomenclature of halo substituted compounds.

Why is it that 1-bromo-3-methylbut-2-ene is named like that and not as 2-(1-bromomethyl)but-2-ene? why do we prefer the carbon chain including the carbon attached to the bromine and not the chain including the carbon of the methyl group?

Which IUPAC rule was used in making this preference between those two carbon chains of equal length?


texts: Is there a way to replace a gas (air) for example with another gas (say, helium) in a gas chamber? It does not need to be a complete replacement, but there would need to be a significant amount of the new gas. Thanks!


texts: When, how and why does sodium metal react with cycloalkenes, cycloalkadienes, cycloalkatrienes?

texts:
I've been searching for the conditions necessary for the reaction of sodium (Na) metal with cycloalkenes, cyclo-di-alkenes, cyclo-tri-alkenes all over the internet but I cannot find a proper answer. Can someone explain to me the necessary conditions?

For example why does sodium metal react with cyclopentadiene but not with cycloheptatriene?


texts: Simple sandbox software for an interactive molecular dynamics simulation

texts:
I'm not sure if this is the right site to ask a such question.  But I'm getting to learn the world of the small.

I know there is software out there like NAMD, and LAMMPS.  But these tools are very non-intuitive, having complex interfaces that seem to hide the underlying mechanics.

I'm looking for something that can display live molecular simulations in 3D, with some kind of inbuilt editor to simply place, or remove atoms.

Again, sorry if this is the wrong place for a such question, I'm sure from what you can tell, I am extraordinarily new to this area of knowledge.  I would greatly appreciate any feedback.  I fear although, I will have to create my own intuitive frontend to NAMD or equivalents to have essentially a 'quantum sandbox'


texts:
I'm an electronic engineer student and I'm trying to understand the basics of electrolytic cells and practical values' meaning. Based on my figure and electrode potencial values (Vce, Vre and Vwe), can you help me how to describe the following concepts:

Standard cell potencial
Equilibrium potential
Overpotential
Open circuit potential
Reference voltage (electrochemical perspective)

EDITED:
Actually I'm asking about direct relations between this definitions and circuit voltages if there are any

For example, is OCP = Vre when it's not applied external potential?

Thank you for your time!


texts: If change in free energy (G) is positive, how do those reactions still occur?

texts:
I was doing a couple of problems for homework:

Calculate $K_\mathrm{sp}$ of $\ce{AgI}$ at $55.0\ \mathrm{^\circ C}$

Calculate $K_\mathrm{b}$ of $\ce{NH3}$ at $36.0\ \mathrm{^\circ C}$

I have to use $\Delta G^\circ= -RT\ln K$ and $\Delta G= \Delta H-T\,\Delta S$

When I did this $\Delta G^\circ$ is positive ($89.59\ \mathrm{kJ/mol}$ and $28.037831\ \mathrm{kJ/mol}$ respectively), yet $K_\mathrm{sp}$ for $\ce{AgI}$ is $5.5\times10^{-15}$ and $K_\mathrm{b}$ for $\ce{NH3}$ is $1.8\times10^{-5}$, indicating that there are some products and the reactions do occur. Plus, $1.0\ \mathrm M$ $\ce{NH3}$ in solution has a $\mathrm{pH}$ of $11.6$ so it must react a little.

According to the second law of thermodynamics, if $\Delta G$ is positive, the reaction is not spontaneous, right? But clearly, they, in fact, are to a certain extent. What is going on?


texts: Does the electrolysis of water produce chlorine gas?

texts:
http://orbitingfrog.com/2014/11/02/electrolysis-of-water-with-pencils-and-a-9v-battery/

This article seems to indicate that "a small amount of Chlorine may be produced as you [perform electrolysis on water]". Is this true? I thought it was just H2 and O2 produced.


texts: Electrochromic Materials, electrode setup

texts:
I've read a lot about electrochromism. This article on electrochromic materials has also been additionally helpful.
I was wondering, for these electrochromic materials, can you simply attach a small electrode to either side of the film like in setup 2, then apply a small voltage? Will the electrochromism only occur at the edges in this case?
Does anyone know how material dependent this effect is? I was hoping to use a polymer film in particular.


texts:
I am studying fuel cells right now and I'm confused about the polarity of the two electrodes.

In the diagram below, the anode is shown as negative. However, why do $\ce{H+}$ ions move away from the anode, when they should be attracted to it because of its negative charge?

On the other hand, if I swapped the polarity around, movement of electrons from the positive to the negative terminal wouldn't work out.

Please explain which polarity is correct, and why.


texts: What is the least dense liquid under normal conditions?

texts: What is the least dense liquid under normal conditions, room temperature, one atmosphere of pressure, doesn't combust upon contact with air, also wouldn't kill a human just for being in the same room as it?


texts:
A few days ago, I learned the lengthy process of salt analysis during my practicals. The process is based on deductive reasoning but is too lengthy.

What I am thinking is, can't it be done using the fact that all molecules have unique emission spectra? I searched for it and found that it's the same thing as the flame test which was covered in my class.

But a flame test is only used for metal ions. So, my question is: Is there a way in which I can determine the metal ion as well as the radical part(anion part) of the salt using spectroscopic methods? What equipment would I need for it?


texts: Why does hydrochloric acid not damage the human stomach?

texts: Hydrochloric acid ($\ce{HCl}$) is found in the stomach, so why it doesn't damage the stomach despite that it is considered to be one of the most dangerous acids?


texts: What is the electrophile in Perkin's condensation reaction?

texts: In Perkin's reaction, an aromatic aldehyde reacts with an acid anhydride to give an alpha-beta unsaturated aromatic acid. Which reactant is the electrophile and which one is the nucleophile?


texts: Diastereoselectivity in the zinc-mediated Barbier allylation

texts:
Penumati & Kommu (2014) report the stereoselective synthesis of (+)-$\alpha$-conhydrine from R-(+)-glyceraldehyde. In their synthesis, the imine 6 underwent a zinc-mediated Barbier allylation to produce secondary amine 7.

They explained the preferential formation of the major product 7a over 7b via the following Felkin-Ahn model, claiming that the anionic allyl nucleophile approaches the less hindered face. However, it appears to me that there is no significant difference in the steric hindrance posed by each face of the imine group. Hence, I am skeptical if application of the Felkin-Ahn model here is appropriate and whether it does give the correct predicted major product. I thought of using the chelation model, since certainly there is a possibility $\ce {Zn^2+}$ can be involved, but I realised that it doesn't seem to be appropriate as well, or at least that is what appears to be the case for me.

Reference

Penumati, N. R.; Kommu, N. Stereoselective Synthesis of (+)-$\alpha$-Conhydrine from R-(+)-Glyceraldehyde. Organic Chemistry International, 2014. doi: 10.1155/2014/982716


texts: After producing nitrogen by distilling air, how is that nitrogen used with the oxygen to yield nitrous oxide ($\ce{N2O}$)? I see $\ce{N2O}$ available in different purities from various suppliers, but how is that different from just distilling air? When distilling nitrogen from air, once both gasses have reached the right temp/pressure to become a liquid, what is preventing it from becoming $\ce{N2O}$ in a liquid form instead of one floating on top of the other? These questions are in reference to an automotive application.


texts: several coefficient differences in UV-vis Spectroscopy

texts: Does anyone know what is scattering coefficient, absorption coefficient and extinction coefficient, and how to separate them experimentally?


texts: Original concentration calculation homework

texts:
A student performs the following gravimetric analysis of iron ions in a water system
$$\ce{Fe^2+  (aq) + CO3^2-  (aq) <=> FeCO3 (s)}$$
If this student used excess carbonate and obtained the following data, what was the original concentration in moles/L) of $\ce{Fe^2+}$ in the water sample?

Total Volume of Solution: 100.00 mL

Mass of $\ce{FeCO3}$ collected: 23.758 grams.

Change 100 ml to 0.1 liters $x + 115.583 = 23.758 \times 0.1 = 0.02~\mathrm{l}$
- would this be how you solve this problem?


texts: Molecular orbital diagram of CO and charge localisation

texts:
MO diagram of CO

My question concerns the interpretation of the Molecular Orbital of CO. I think I find it clear how you build it but I have some concerns about how you rationalize it.

Particularly, from what I read the reason we envision carbon as being partially negatively charged in CO is that the HOMO of the molecule lies closer to the carbon orbitals. However, from the MO diagram, it can be seen that the p-oxygen orbitals are closer to the HOMO than both of the orbitals of carbon.

My question is: what we use as a benchmark to judge that the HOMO is closer in to energy carbon: are we looking at average energy or something completely different and I completely misinterpreted the argument?


texts: Confusion regarding mechanism of dehydration of alcohols

texts:
1)Today I came across a problem which asks to find the order of dehydration of 2-hydroxycyclohexanone(1), 3-hydroxycyclohexanone(2),4-hydroxycyclohexanone(3). The answer is 2>3>1 But I thought answer should be 2>1>3 cause in 2 and 3 the product would be conjugated and hence more stable.
2)My second confusion is regarding the pathway taken by such hydroxyketones. Do they follow E1 pathway and form carbocation or do they take some other pathway?

I have provided what I think but I am not sure whether the same mechanism will be followed or not.


texts: Hydrogen and Helium ideal gas behavior in room temperature

texts:
Which one of hydrogen and helium behaves more like ideal gas in room temperature...

I thought hydrogen gas would show more ideal behavior in room temperature because it has lighter mass (less no of electron) although it's diatomic, so there would be less attraction.
However, I saw one question on the book and they said that the helium gas is more likely to show the ideal gas behavior in room temperature, not the hydrogen gas..

So, can someone please give me an idea how my thinking is wrong?.

Thanks for advance


texts: Separating sodium sulfate from chromium trioxide solution

texts:
I was looking at the industrial process for the production of chromium trioxide by treating sodium chromate or the corresponding sodium dichromate with sulfuric acid. This results in the formation of chromium trioxide as well as sodium sulfate. I think both of them would be mixed as a solution; so what way is employed to separate them? I read about the process in Wikipedia.
I thought of using methods which I know like distillation, but I don't know how can I check if they work practically and are employed industrially. I searched the web as well and couldn't find anything satisfactory.
I am in 12th grade and I haven't really studied this topic, so I didn't know how to approach this question.


texts:
I have a basic question about how water dissolves salt. In the Khan Academy explanation, it says that the H and Cl atoms attract each other while the O and Na atoms attract each other.

My question: Does this weaken the bond between Na and Cl within a single NaCl molecule? Or does it weaken the bonds between Na of one molecule and Cl of another salt molecule? Or does dissolution weaken both?


texts: What liquid other than water that is safe to put on your skin will provide the most evaporative cooling?

texts:
Suppose that you are in some extremely hot and humid place where your sweat just doesn't evaporate well enough to cool you down. You can then consider putting a liquid other than water on your skin, e.g. methanol would be an excellent liquid with a decent latent heat and high rate of evaporation at room temperature, but this is poisonous. Ethanol is better, but it will also cause problems as you need to use large quantities.

The question is then what liquid that can be used safely, will provide the best cooling.


texts: Why is perchloric acid stronger than perbromic acid?

texts: Since chlorine has a larger electronegativity than bromine, why is perchloric acid a strong acid, while perbromic acid is not?  We clearly see that electronegativity affects an acid's strength with hydrofluoric acid being much weaker than hydrochloric acid, due to fluorine's high electronegativity.  Wouldn't chlorine's higher electronegativity make it harder for perchloric acid to dissociate than perbromic acid like it does for hydrofluoric acid?


texts:
Suppose I have a small kid that had two cans of slime jelly (a Jelly made of water, glycerin, thickeners, dispersant, flavorings and pigments).

And that two cans were inside a backpack, and somehow opened and spread in the bottom. Involving some dolls, small toy cars, entrancing in some holes. Even after trying physical processes not all jelly could be removed.

Adding water and soap did not difference, as jelly is still there, and even the two colors haven't mixed.

How can I dissolve those jelly, preferably leaving the nylon backpack, the metal cars and the plastic dolls without significant damage?


texts:
This is from my textbook.
But in other reference books I am using and Wikipedia, there is not any mention of absolute zero while defining Ionization Energy and Electron Affinity.
What does it mean? Please Elaborate


texts:
I hope this doesn't sound too strange.
I have plenty of cheap vodka and want to clean the A/C on my car.

So I thought about boiling 1/2 litre of vodka in my car while I ran the A/C with recirculation on.
The alcohol should get liquid within the air conditioner and desinfect and clean the vaporizer.

I am just not sure if I create an explosive mixture inside the car this way.

David


texts:
I have five values for the volume of sodium hydroxide needed to neutralise a fixed quantity of hydrochloric acid, each trial with an uncertainty of 0.05 mL. If I take the average of these five values, in what way would the uncertainty propagate? I can think of three of the following ways, but don't understand which would be correct:

Because we can see the calculation of an average as the sum of the values for the five trials (with their uncertainties), and then a division by 5, we sum up the uncertainty to get 0.25 mL and then divide it by 5 to get the uncertainty of the average to be 0.05 mL.
Because we can see the calculation of an average as the sum of the values for the five trials (with their uncertainties), and then a division by 5 (which has no uncertainty), we sum up the uncertainty to get 0.25 mL and then divide it by 5 to get the uncertainty of the average to be 0.25 mL.
Range divided by two is often another way to calculate the uncertainty of an average value, which for my case results in a value different to the above two for the uncertainty of the average.

Which one, and why, would be the correct one to state next to the average value (with a plus-minus sign), as an uncertainty of the average value?


texts:
My thermos bottle's instructions say:

  Füllen Sie keine kohlensäurehaltigen Flüssigkeiten oder Trockeneis in das Produkt. Füllen Sie keine alkoholischen oder öligen Flüssigkeiten in das Produkt.

This translates to:

  Do not fill carbonated liquids or dry ice into the product. Do not fill alcoholic or oily liquids into the product.

I suppose the reason you're not supposed to fill carbonated liquids or dry ice into the thermos bottle is that the bottle isn't able to handle the pressure which builds up if you close the lid. In the case of dry ice, it might also not be able to cope with the temperature of it. I further suppose that oil can wear down the seal.

But why are you not supposed to store alcohol in it? Sure, some alcoholic beverages are carbonated, but those already are excluded. What about beverages like mulled wine?


texts: Why and how do we get NH4NO3 when reacting very dilute HNO3 with Zn?

texts:
From Russian Wikipedia's article on nitric acid:

It's clear that as we decrease the concentration of nitric acid, we get more and more reduced nitrogen: in $\ce{NO2}$, the oxidation state of N is ($\mathrm{+4}$), then it goes to zero in $\ce{N2}$ (when we use $\mathrm{10\%}$ strong $\ce{HNO3}$).

But why all of a sudden we get $\ce{NH4NO3}$? In $\ce{NH4}$, the oxidation of $\ce{N}$ is ($\mathrm{-3}$), in $\ce{NO3}$, the oxidation state is ($\mathrm{+5}$). So the overall oxidation increases by $\mathrm{2}$.

I wonder how this ammonium nitrate is generated, i.e. where the ammonium ion evolves from.

P.S. Got an answer on Socratic.


texts: How would you add saccharide residue information to PDB files?

texts:
I have multiple PDB files containing a single molecules of polysaccharides, with a single chain and a long list of all the atoms -they are not divided by residue.
The PDB files were created from ChemDraw files using OpenBabel and Corina applet form molecular-networks. The workflow was: .cdx <-> OpenBabel <-> smiles/sdf <-> Corina <-> pdb.
What i end up with is this:

How do i easily break up the list into individual residues(individual monosaccharides)? I trying to something similar to 1CAP

This is what the PDB file looks like after CORINA:

HEADER    UNK                                     15-05-08    1UNK
REMARK   1 corina 3.48 0000  08.02.2010
HETATM    1  C1  UNK     1       6.576  -2.524   4.463  1.00 20.00
HETATM    2  H2  UNK     1       6.573  -2.048   5.444  1.00 20.00
HETATM    3  C3  UNK     1       5.876  -1.614   3.449  1.00 20.00
HETATM    4  C4  UNK     1       4.411  -1.438   3.863  1.00 20.00
HETATM    5  C5  UNK     1       3.748  -2.815   3.964  1.00 20.00
HETATM    6  H6  UNK     1       3.760  -3.296   2.986  1.00 20.00
HETATM    7  O7  UNK     1       4.467  -3.621   4.900  1.00 20.00
HETATM    8  C8  UNK     1       5.829  -3.859   4.541  1.00 20.00
HETATM    9  C9  UNK     1       6.487  -4.751   5.595  1.00 20.00
HETATM   10  O10 UNK     1       5.864  -6.037   5.587  1.00 20.00
HETATM   11  O11 UNK     1       2.398  -2.662   4.404  1.00 20.00
HETATM   12  C12 UNK     1       1.655  -3.882   4.435  1.00 20.00
HETATM   13  C13 UNK     1       0.198  -3.584   4.795  1.00 20.00
HETATM   14  C14 UNK     1      -0.566  -4.899   4.964  1.00 20.00
HETATM   15  H15 UNK     1      -0.496  -5.481   4.045  1.00 20.00
HETATM   16  C16 UNK     1      -2.036  -4.592   5.265  1.00 20.00
HETATM   17  C17 UNK     1      -2.607  -3.729   4.136  1.00 20.00
HETATM   18  C18 UNK     1      -1.764  -2.458   4.000  1.00 20.00
...
...
HETATM  286  H   UNK     1      14.974  11.280   1.314  1.00 20.00
HETATM  287  H   UNK     1      15.417  11.215  -0.409  1.00 20.00
HETATM  288  H   UNK     1      15.300  13.559   0.392  1.00 20.00
HETATM  289  H   UNK     1      14.052  13.241  -0.836  1.00 20.00
HETATM  290  H   UNK     1      13.609  13.306   0.886  1.00 20.00
HETATM  291  H   UNK     1       9.253  -4.179   6.144  1.00 20.00
HETATM  292  H   UNK     1      11.359  -2.412   4.593  1.00 20.00
CONECT    1    2    8    3  115
CONECT    2    1
CONECT    3    1    4   86  120
CONECT    4    3    5   69  121
CONECT    5    4    6    7   11
CONECT    6    5
CONECT    7    5    8
CONECT    8    7    1    9  122
...
CONECT  289  114
CONECT  290  114
CONECT  291  118
CONECT  292  119
END


texts: Symbolic form of equilibrium constant for ammonium carbamate dissociation

texts:
$$\ce{NH2COONH4(s) <=> 2 NH3(g) + CO2(g)} \qquad K = \left(\frac{p(\ce{NH3})}{p^\circ}\right)^2\times\frac{p(\ce{CO2})}{p^\circ}$$
Assuming that you start this experiment with pure solid $\ce{NH2COONH4}$ in an evacuated container and allow it to dissociate until equilibrium is reached, show that the equilibrium constant can be rewritten as
$$K = \frac{4}{27}\left(\frac{p_\mathrm{tot}}{p^\circ}\right)^3.$$

Let $n_0$ be the initial amount of ammonium carbamate and $\alpha$ be the factor describing the extent of dissociation:
$$
\begin{array}{cccccccc}
\ce{&NH2COONH4(s) &<=> &2 NH3(g) &+ &CO2(g)} &\quad &\text{Total}\\
& n_0 && 0 && 0 && n_0\\
& (1 - \alpha)n_0 && 2\alpha n_0 && \alpha n_0 && (1 + 2\alpha)n_0\\
\end{array}
$$
We can express mole fraction $x_i$ and partial pressures $p_i$ for $i$th component as follows:
$$x(\ce{NH2COONH4}) = \frac{n(\ce{NH2COONH4})}{n_\mathrm{tot}} = \frac{(1 - \alpha)n_0}{(1 + 2\alpha)n_0} = \frac{1 - \alpha}{1 + 2\alpha}\tag{1}$$
$$x(\ce{NH3}) =  \frac{n(\ce{NH3})}{n_\mathrm{tot}} = \frac{2\alpha}{1 + 2\alpha}\tag{2}$$
$$x(\ce{NH3}) =  \frac{n(\ce{CO2})}{n_\mathrm{tot}} = \frac{\alpha}{1 + 2\alpha}\tag{3}$$
$$p(\ce{NH3}) = x(\ce{NH3})\cdot p_\mathrm{tot} = \frac{2\alpha p_\mathrm{tot}}{1 + 2\alpha}\tag{4}$$
$$p(\ce{CO2}) = x(\ce{CO2})\cdot p_\mathrm{tot} = \frac{\alpha p_\mathrm{tot}}{1 + 2\alpha}\tag{5}$$
Finally, plugging in the partial pressures into the given expression for the equilibrium constant:
$$
\begin{align}
K &= \left(\frac{p(\ce{NH3})}{p^\circ}\right)^2 \times \frac{p(\ce{CO2})}{p^\circ} \\
  &= \left(\frac{2\alpha p_\mathrm{tot}}{(1 + 2\alpha)p^\circ}\right)^2 \times \frac{\alpha p_\mathrm{tot}}{(1 + 2\alpha)p^\circ} \\
  &= \frac{4\alpha^3p_\mathrm{tot}^3}{(1 + 2\alpha)^3(p^\circ)^3} \tag{6}
\end{align}
$$
This leads me to the right answer if I make an assumption that all of the ammonium carbamate dissociates. The question doesn’t say I could do this, hence why I’m not sure how to proceed. Any suggestions are greatly appreciated for deriving this.


texts:
We know that an activation complex is the temporary unstable compound formed when activation energy is reached. But what dictates whether the products are indeed going to be products or if they become reactants?

Does the activation complex form when orientation is both correct and incorrect, and only forms products when the orientation is correct? Or is the decomposition of the complex purely a chance matter?


texts:
Why is spin-contamination, introduced by e.g. Unrestricted Hartree Fock, undesirable, and to which problems further on can it lead?

The only problem I currently see myself is that spin-contamined orbitals cannot be used in spectroscopy, because the selection rules don't hold.


texts: Calculating the dissociation constant of one acid in a mixture

texts:
A solution contains $\pu{0.09 M}~\ce{HCl}, \pu{0.09 M}~\ce{CHCl2COOH}$ and $\pu{0.1 M}~\ce{CH3COOH}$. The $\mathrm{pH}$ of the solution is $1$. Given that the $K_\mathrm{a}$ of acetic acid is $10^{-5}$, calculate the $K_\mathrm{a}$ of $\ce{CHCl2COOH}$.

My attempt is as follows. We have $[\ce{H+}] \text{ from } \ce{HCl} = [\ce{HCl}] = \pu{0.09 M}$.

Then, for the other two acids:

$$\begin{align}
[\ce{H+}] \text{ from } \ce{CH3COOH} &= x \\
\frac {10^{-2}\cdot x^{2}}{10^{-1}-x} &= K_\mathrm{a} \\
[\ce{H+}] \text{ from } \ce{CHCl2COOH} &= y \\
\mathrm{pH_\text{total}} &= 1 \\
-\log_{10}(0.09+x+y) &= 1 \\
0.09+x+y &= 10^{-1} \\
\end{align}$$

But the answer key says the answer is $\pu{1.25*10^{-2}}$.


texts: After research I found that enzymes are responsible for metabolism, specifically catabolism and anabolism. This in turn creates the necessary chemicals in your body. The only question left is: what are enzymes? I asked in Biology and the answer led me to enzymes being created by ribosomes. Ribosomes by RNA. RNA by the four chemicals, adenine, guanine, cytosine, and uracil. Okay so, my question is: what chemical elements are those four chemicals comprised of?


texts: Computing van der Waals constants from molecular structure

texts:
How can van der Waals constants be computed from molecular structure?

Is there software that already does this?

Is there software that can design a molecule with specified van der Waals constants?

This relates to the question
Fluids with critical point at ordinary temperature and pressure


texts: I know PV=nRT but that's total what about partial?

texts:
What is the formula for finding the partial pressure ?
I know PV=nRT but that's total what about partial ?


texts:
I am having problem predicting the last product in the following reaction:

  $$\ce{CH#CH ->[Na/NH3 (l)][(Excess)] (P) ->[DCl] (Q) ->[(i)Sia2BH][(ii)CH3COOH] (R)}$$

I am getting an alkyl chloride as product $\ce{Q}$ and cannot understand how it will react with $\ce{Sia2BH}$. Or, I think I am doing some mistake in the formation of product $\ce{P}$. I do know that alkynes on reaction with $\ce{Na/NH3}$ shall give trans alkene (Birch reduction). Will the "excess" part affect the reaction differently?

$$
\begin{align}
\ce{CH#CH &->[Na/NH3 (l)][(Excess)] CH2=CH2} &(\ce{P}) \tag{1} \\
\ce{CH2=CH2 &->[DCl] CH2D-CH2Cl} &(\ce{Q}) \tag{2} \\
\ce{CH2D-CH2Cl &->[(i)Sia2BH][(ii)CH3COOH] ?} &(\ce{Q}) \tag{3}
\end{align}
$$


texts: What if solute and solvent exist in equal quantities?

texts:
A solution is made of solute and solvent, like salt in water, however, what if the solute and solvent exist in equal quantities?
Which one is the solute and which is the solvent? If one of them is water I think it will definitely be the solvent, but what if neither of the two parts are water?


texts: What is symmetry of p- and d-orbitals in ${D_{3h}}$?

texts:
To identify IR and Raman active, symmetry of p- and d-orbitals are used.

If we start since making ${D_{3h}}$ character table, how to match between symmetry of p- and d-orbitals and Mulliken symbol? because when I tried to find out, symmetry after doing symmetry operation isn't similar with any symmetry (Mulliken symbols).

For example, considering ${AsCl_5}$

compared with ${D_{3h}}$ character table


texts: What is the number of unpaired electrons in Fe 2+?

texts: Specifically, how can I find out the number of unpaired electrons in any ion?


texts: Gaussian calculation problem - Maxcycle values for Opt and SCF

texts:
I've been trying to calculate vertical ionization potentials (IP) and electron affinities (EA) for a bunch of prostaglandin derivatives (23-25 heavy atoms). My calculation setup in Gaussian09 looks mostly like that:

# opt=(tight,maxcycle=1000)
freq=noraman cphf=noread
b3lyp/6-31g(d) geom=connectivity
integral=grid=ultrafine scf=maxcycle=1000

As you can guess, I have been struggling with converging the geometry and finding the stationary point for my molecules. Some were kind of stubborn and wouldn't converge, so in desperation I increased the Maxcycle values for Opt and SCF from a 1000 up to 5000, and I succeeded with some of them. Now, my question is if I need to recalculate all other prostaglandins that have already nicely converged with lower Opt(Maxcycle) or SCF(Maxcycle) options (I used them in different combinations like 1000, 3000 and 5000)? The thing is that I want to be able to objectivelly compare the IP and EA values between different derivatives.

I am concerned because I remember that someone told me that if I went for SCF=QC option I would need to recalculate the whole set of molecules with the same keyword option. However, as far as I know SCF=QC is like a substantial change in the setup as it uses another algorithm for calculations. Hopefully, changing the SCF(Maxcycle) value is not that dramatic, is it? How about SCF=Verytight - would it demand recalculating everything or not?

Another thing that bothers me is Opt=Tight. What if I decided to go for Opt=Verytight. Would I need then to recalculate all of the molecules with the same setting?

And lastly, what if I changed Integral(grid=ultrafine) to Integral(grid=ultrafine, acc2e=12) which is supposedly the most precise approach?


texts: Directing nature of the -SOR substituent in electrophilic aromatic substitution

texts:
This is (alkanesulfinyl)benzene:

I didn't draw it, but we know that the sulphur atom also has a lone pair. So, the sulphur atom can increase electron density in the ring by donating a lone pair. However, oxygen can also withdraw electron density from the ring by pulling back an electron pair. They both are contradictory, so which effect dominates? What is the final directing effect of the alkanesulfinyl group?

That said, I am not entirely sure if what I said above is 100% correct. The reason being that since the sulphur atom is sp3 hybridized, it is tetrahedral in shape, and not planar. So, either the sulphur's lone pair or the oxygen's pi bond will be out of the plane (but not both at once), and won't take part in any delocalisation. But we can't theoretically predict which one it would be, can we?

If there could be experimental evidence to support the claim whether it is meta-directing or o/p-directing, that would be even more beneficial. I have checked both Wikipedia and masterorganicchemistry, and neither even mentions this functional group, let alone its directional nature.


texts: Conservation equation of reaction scheme

texts:
Consider the reaction scheme:

$$\ce{S + E ->[k_1] C1} \qquad \ce{C1 ->[k_2] E + P} \qquad \ce{S + C1 <=>[k_3][k_4] C2}$$

where $\ce{S}$ is the substrate, $\ce{E}$ is the enzyme, $\ce{P}$ is the product, $\ce{C1}$ and $\ce{C2}$ are enzyme substrate complexes. Let $[\ce{S}] = s$, $[\ce{E}] = e$, $[\ce{C1}] = c_1$, $[\ce{C2}] = c_2$ and $[\ce{P}] = p$ be the concentrations of each respective chemical. I have used the law of mass reaction to convert this reaction into a system of differential equations:

\begin{align}
\frac{\mathrm{d}s}{\mathrm{d}t} &= -k_1se-k_3sc_1+k_4c_2\\
\frac{\mathrm{d}e}{\mathrm{d}t} &= -k_1se+k_2c_1\\
\frac{\mathrm{d}c_1}{\mathrm{d}t} &= k_1se-k_2c_1-k_3sc_1+k_4c_2\\
\frac{\mathrm{d}c_2}{\mathrm{d}t} &= k_3sc_1-k_4c_2\\
\frac{\mathrm{d}p}{\mathrm{d}t} &= k_2c_1
\end{align}

I notice that

$$\frac{d}{dt}(e+c_1+c_2) = 0.$$

Hence $e+c_1+c_2 = const.$ Now is this a conservation equation? Also how do I use this equation to simplify the system?


texts: Relative energies between reactants and products

texts:
I've been asked to draw a relative energy sketch of the reactants and the two products. The reaction being examined was adding copper acetate monohydrate to glycine in two different fashions to create the two isomers cis-bis(glycinato)copper(II) monohydrate and trans-bis(glycinato)copper(II) monohydrate. I found that the cis-bis(glycinato)copper(II) monohydrate was  thermodynamically stable and trans-bis(glycinato)copper(II) monohydrate was kinetically favored since when adding heat to trans-bis(glycinato)copper(II) monohydrate it changed to the same color as cis-bis(glycinato)copper(II) monohydrate therefore cis-bis(glycinato)copper(II) monohydrate has a lower energy relative to trans-bis(glycinato)copper(II) monohydrate. The part where I'm stuck is where the reactant energy is relative to these two. I know it must be lower than the intermediate trans-bis(glycinato)copper(II) monohydrate, but where the energy level of the reactants compared to the thermodynamically stable cis-bis(glycinato)copper(II) monohydrate has me stumped, whether it is higher or lower.

Cheers


texts: Does standard electrode potential of a reaction depend on stoichiometric coefficients?

texts:
Take a reaction like this

$$\ce{Fe^3+ + 3e- -> Fe}$$

now will the standard electrode potential change if we take 2 moles of $\ce{Fe^3+}$ and 6 moles of electrons?

$$\ce{2Fe^3+ + 6e- -> 2Fe}$$


texts: Can ethylene glycol enhance the acidity of orthoboric acid?

texts:
My textbook says:

  Boric acid is a weak monobasic acid but on addition of certain organic polyhydroxy compounds, such as mannitol, glycerol, dextrose or invert sugar, it is transformed into a relatively stronger acid. Ethylene glycol cannot give this test (reason is uncertain).

I do know that cis-diols form a boron-ether compound with the $\ce{[B(OH)4]-}$, leading to an increase in acidity. But is it true that ethylene glycol is exceptional? And is there any possible reason for it?


texts:
What will happen when $\pu{1 mol}$ of $\ce{H2SO4}$ reacts with $\pu{1 mol}$ of $\ce{NaOH}$?

Will $\pu{1 mol}$ each of $\ce{NaHSO4}$ and water be formed?

Or will $\pu{0.5 mol}$ of $\ce{H2SO4}$ will remain yield $\pu{0.5 mol}$ of $\ce{Na2SO4}$ and $\pu{1 mol}$ of water?

I believe it will be the second way since H2SO4 is a strong acid and would again quickly react with the $\ce{NaHSO4}$ formed. But I am not quite sure how the mechanism will be and whether the Rate constant of the second reaction will be high enough to facilitate this.

What will happen and why?


texts: Why is a ketone more nucleophilic than an ester?

texts: I guess the ester is a weaker nucleophile because it does have an additional oxygen atom, unlike the ketone, that is pulling electrons from the C-O double bond towards the carbon atom (this happens vice versa too of course with the ester oxygen). This lowers the ionic character of the C-O double bond (smaller $\delta^{+}$ and $\delta^{-}$ charge on the carbon and oxygen atoms) and thus increases the energy of the C-O $\pi^{*}$ bond, making it less nucleophilic.   Is this correct?


texts: Is there a systematic naming system to name carbonyl derivatives?

texts:
I had asked a question earlier about how the “$\ce{-COOCl}$” functional group would be named.

I had received a satisfactory answer that helped me completely understand how that compound was named.

However, I have a much broader question in mind now.

Consider the "$\ce{-COOH}$" functional group. We know that it's called a carboxylic acid group, however I used to think, why wasn't ethanoic acid simply called as a 1-hydroxyethanal? I now know that "1-hydroxyethanal" has properties vastly different from both aldehydes and alcohols, and as a result, was named differently to acknowledge this difference. Many acid derivatives have been named (and behave) differently, as a result of the $\ce{C=O}$ group nearby.

However, these may not be the only molecules that are affected by the nearby $\ce{C=O}$ group. My earlier question had dealt with the $\ce{-COOCl}$ functional group (not to be confused with acyl chloride $\ce{-COCl}$). However, there are a lot more:

Of course, I did try to name these compounds myself.

Cyanide is sometimes treated as a pseudohalide, so my guess is ethanoyl cyanide.
It may be an anhydride of hydrogen sulfide and ethanoic acid, but I'm not very sure.
Loong gave me an interesting way to name certain "anhydride" compounds in my previous question. This looks like an anhydride of hydroxylamine and ethanoic acid. So according what Loong told me, my guess is ethanoic hydroxylamine anhydride.
This one look's rather crazy to me. Had this been posessing a $\ce{C-O-S}$ instead of a $\ce{C-S}$, this would have been an anhydride of sulfuric acid and ethanoic acid. But it's not, so I have no clue on how to name it.
This one looks very familiar to an amide, infact a phosphorus analog of amide. For some reason, I feel like calling it ethanephosphide, although I don't know why.
Like cyanide, even azide is considered a pseudohalide, so my guess is ethanoyl azide.

Please keep in mind, I am not asking for the explanations to the naming of all the six compounds I showed above, although it would be great if I could get the names alone. Rather, what I mean to ask is is there any simplified nomenclature that can deal with all these types of compounds in a simple way? Although I only showed six, I can go on as long as my imagination permits.


texts: Will SnO2 or SnO form from this reaction?

texts:
I have two possible chemical equations for a reaction between $\ce{SnCl2}$ and $\ce{H2O}$. The first one is:

$$\ce{2SnCl2 + 2H2O +O2 -> 2SnO2 + 4HCl}$$

where the reaction draws on oxygen from the air. The second possibility is:

$$\ce{SnCl2 + H2O -> SnO + 2HCl}$$

I know that in the first reaction, tin is oxidized and oxygen is reduced, but I can't figure out if that reaction is favorable, or if it is possible that it's using oxygen from the air. The second equation is the only other possible reaction that I can find, but it doesn't form the product that we want.


texts:
My textbook says that $\ce{C_2}^-$ has a lower ionization energy than both $\ce{C_2}$ and $\ce{C_2}^+$. I calculated that the bond orders of $\ce{C_2}^+$, $\ce{C_2}$, and $\ce{C_2}^-$ are 1.5, 2, and 2.5, respectively.

Why doesn't $\ce{C_2}^-$ have a higher ionization than the other two molecules? Shouldn't the molecule with the larger bond order have the larger ionization energy, because it would be more difficult to remove an electron from the stable bond?


texts: Number of chiral centers in penicillin V

texts:
I have often seen that in many drugs chirality plays a role. So I was trying to analyze the structure of Penicillin V.

What is number of chiral centers in the structure of penicillin V? Is the nitrogen which is  a part of the four membered ring to be counted here because I have read that the nitrogen atom without pyramidal inversion is treated as chiral. So can the nitrogen at bridgehead position be treated as chiral? Because that makes the stereocenter count 4 while on pubchem website the count is mentioned  to be 3.


texts:
Is oxygen really necessary for burning things?

What if there was no oxygen around? Would there still be a way to burn things?


texts:
I have recently been trying to come up with a method to synthesize 2-methyl-2-butanol or tert-amyl alcohol. I wish to avoid complex/expensive steps since as a home chemist/student, I don't have access to much money or equipment.

What I have done so far: I noticed that methyl ethyl ketone has pretty much the correct structure, minus a methyl group.

I then realized this meant I could use a methylating agent to get the correct molecule. What I needed was to break the $\ce{C=O}$ bond from the carbonyl group and add a methyl group.

Long story short, I found that either Grignard reagents or something like methyl lithium would do it since it would donate an electron pair to the carbon, and form a bond with the methyl. I would then have the 2-methyl-2-butanol as a conjugate base with $\ce{Li}$ ions present. I could then react them out with $\ce{HCl}$ to precipitate out the $\ce{Li}$ salt and add a hydrogen to the negatively charged oxygen.

My problem: I don't know if this would work at all. I didn't find any documentation. Also, methyl lithium is very expensive and difficult to make so I can't use it.

Does anyone have any other route suggestions? Would it be possible to make methyl sodium and if so, would it work the same? Is it possible to make Grignard reagents easily at home?

I'm a hobby chemist, so please be detailed with how you predicted the organic reaction.

Also, I don't necessarily care about what chemicals I use for the reaction, so if anyone can suggest a different starting chemical, I'd be glad to hear it. I was even thinking of using an alkene group of some kind and methylating the $\ce{C=C}$ bond, but I don't know for sure, as I'm pretty new to organic chem.


texts: Calculating mass of krypton from mole fraction

texts:
There are two gases in a container: krypton and carbon dioxide. If the mass of the gases is 35 grams, and total pressure of the container is 0.708 atm, and the pressure of krypton is 0.250 atm. What is the mass of the krypton?

I've found the mole fraction of krypton is 0.3531. First, I think if I multiply mole fraction of krypton and mass of the gases, I'd get the mass of krypton. But my teacher said if the answer is false. So what is the correct answer?


texts: Why would substitution of H with D alter chemical shift?

texts: The $\ce{^{119}Sn}$ chemical shift of the dimeric tin hydride shown below (R=terphenyl) changes on addition of $\ce{D2}$ from a 1:2:1 triplet at $\pu{657.9 ppm}$ (due to coupling between $\ce{Sn}$ and bridging $\ce{H}$) to a doublet at $\pu{650.6 ppm}$. I assume that's because of reversible dissociation of one of the bridging $\ce{H}$, which allows formation of a mixed species where both $\ce{H}$ and $\ce{D}$ are present (the doublet being due to coupling with the remaining $\ce{H}$). However, I'm not quite certain why that alters the $\ce{^{119}Sn}$ chemical shift (I know the $\ce{Sn-D}$ bond will be shorter/stronger due to the lower ZPE). I would be interested in any thoughts/comments.


texts:
We know that methyl ketones and secondary alcohols oxidizable to methyl ketones, such as isopropanol. The only primary alcohol and aldehyde to undergo this reaction are ethanol and acetaldehyde, respectively. 1,3-Diketones such as acetylacetone also give the haloform reaction.
Do Terminal Alkynes give Haloform Reaction if Yes then how the mechanism will follow?


texts: Spontaneity of Reactions- Gibbs Energy or Entropy change

texts:
I just wanted to check if I am thinking right:

The reason why we consider the Gibbs energy to be the measurer for spontaneity of a reaction is because it does not depend whether the reaction was exo- or endothermic.

Is it arising because:
 if the change in entropy were less than zero, the Gibbs change in energy is less than zero? So if that were true, then entropy may not be a measurer for spontaneity, correct?


texts: Equilibrium constant expression for heterogeneous equilibrium

texts:
Consider this reaction:

$$\ce{CaCO3(s) <=> CaO(s) + CO2(g)}$$

for this, $K_c=\left[\ce{CO2(g)}\right]$

For a given temperature, $K_c$ will remain fixed. That means, the  amount of $\ce{CO2}$ released will be same, irrespective of amount of $\ce{CaCO3}$ taken.

But, that means, at the same temperature, irrespective of  whether we start with 1 g of $\ce{CaCO3}$, or 10 kg of $\ce{CaCO3}$, the amount of $\ce{CO2}$ at equilibrium will be same(!) because, according to the $K_c$ expression, it should be constant.

This is against my intuition, because, it seems that if we start with 10 kg of $\ce{CaCO3}$, we should end up with a much larger amount of $\ce{CO2}$ at equilibrium than if we started with just 1 g of the carbonate.

Am I being mistaken somewhere, or is this is what will actually happen? I am confused.


texts: Equilibrium involving both gas phase and aqueous phase

texts:
If I have been given an equation that involves a gas-aqueous phase equilibria, how do I write the equilibrium constant?

I have come across several questions that give equations having BOTH gas and the aqueous phase and I couldn't comprehend how to attempt them.

Should we find the concentrations of the gas too and use it for the equilibria?

But in several questions I was given partial pressure of the gas at equilibrium but I was never given the temperature to find concentration.

What is a proper way of representing the equilibrium constant?

Here is an example:

$$\ce{RNH2(g) + H2O(l) <=> RNH3+(aq) + OH-(aq)}$$

How do I write the equilibrium constant for this, if I have been given concentrations of $\ce{RNH3+(aq)}$ and $\ce{OH-(aq)}$ and the partial pressure of $\ce{RNH2}$ at equilibrium?


texts: Is there an easy way to make PVC from PVA?

texts:
Say, I took Elmer's glue (or a similar Polyvinyl Acetate) and I inserted some Chlorine Tabs and warm it up while stirring.

Would the electronegative Chlorine turn some of it it into Polyvinyl Chloride (PVC)?

Would I get a Dioxin Compound too?

Would I get any other toxic Side-Product?


texts: How does toluene react at higher temperatures and why?

texts:
Reaction of toluene at high temperatures gives us (o-m)toluene; whereas at normal conditions of electrophilic attack, it gives us (o-p) directing.

Why does this happen at high temp although as methyl group is activating and o-p directing?


texts: Electrolysis in Electrophoresis of proteins and DNA

texts:
Can electrolysis happen in an electrophoresis assay (such as SDS-PAGE)?
To perform electrophoresis, the substances must be dissolved in an aquatic buffer with a previously determined ionic strength. One might expect to see $\ce{H2}$ and $\ce{O2}$ on each side of the electrodes as well as $\ce{H2}$ and $\ce{Cl2}$ (resulting from electrolysis of $\ce{H2O}$ and $\ce{NaCl}$ respectively). Does this actually happen or it is somehow prohibited in the experiment? If yes, then how do manufacturers reduce the effects of such additional reactions in the electrophoresis apparatus? If no, what principles of electrochemistry have I forgotten to consider?


texts: Molar absorption coefficient for potassium hydrogen phthalate

texts:
I would like to draw a comparison of the sensitivity between several spectrometers. Therefor I measure the absorption of a serial dilution of potassium hydrogen phthalate (KHP). The idea is to compare the theoretical absorption with the measured absorption.

To calculate the theoretical absorption I need the molar absorption coefficient of KHP at 254 nm wavelength. Unfortunately I haven't found anything till now.

Does anyone know where I can find this coefficient?


texts: I have the first part correct; however, I can't seem to understand what the 2nd part's answer is. I realize the water leaves, but then what?


texts:
My teacher didn't answer this properly:

  Is toothpaste solid or liquid?

You can't say toothpaste is a solid because solid material have a fixed shape but toothpaste doesn't. However, you can't say it's a liquid because liquids flow easily but toothpaste needs a certain force to push it out of the tube. So is it a solid or liquid? And are there any other example just like toothpaste?


texts: Entropy of solid, liquid, and gas at triple point of water

texts:
At the triple point of water how do the entropies of solid,
  liquid, and gas compare?

I think that either they will be equal or it will be that gas > liquid > solid.

I don't know if entropy is influenced by the fact that it will be at the triple point. Can someone please elaborate?


texts: Reaction of dihalides with excess of NaNH2

texts:
Gem-dihalides react with $\ce{NaNH2}$ to give terminal alkynes. Why is a terminal alkyne prefered?

For example,

I had thought that 2-pentyne would be preferred over 1-pentyne as it would be more stable due to hyperconjugation, but it says the final product is terminal alkyne.

Why?


texts: Recovering from a bottle of ferrous chloride

texts:
My bottle of ferrous chloride powder/crystals was years in shelf and it turned dark brown. If I break up the clumps I can see a little bit of yellow layers. I suspect it's a combination of iron oxide and ferric chloride.
I want to convert it back to green ferrous chloride and I'm looking for cheap ways to do that. My first idea is to dissolve it and stir it with nails, but I find it hard to dissolve in water. I'm not sure if adding HCl helps but it's too expensive for converting the whole 500g.
Better options or ideas?


texts: Why do molecules have to first transform to gas before doing a reaction?

texts:
I have to calculate the enthalpy of the reaction
$$\ce{Cs(l) + 1/2I2(s) -> CsI(s)}$$
and the answer is
$$\Delta H_f = \Delta H_{vap}^{\ce{Cs}} + \frac{1}{2}\Delta H_{subl}^{\ce{I2}} + \frac{1}{2}E_{diss}^{\ce{I2}} + I_1^{\ce{Cs}} + E_A^{\ce{I}} + E_N.$$
I can see that the molecules are first put to gas state before creating an ionic bond.

Why does it have to do it ?
In which case do the molecules have to first go in gas state before reacting ?
Is it only in case of ionic bond ?

Notes:

$E_{diss}$ is the energy of dissociation between the to atoms $\ce{I}$.
$I_1$ is the energy of first ionisation.
$E_A$ is the energy of electron affinity.
$E_N$ is the energy of neutralisation between $\ce{Cs+}$ ans $\ce{I-}$.


texts: What does iron (III) get reduced to in a galvanic cell: solid iron or iron (II)?

texts:
Recently, I built a galvanic cell in the lab with iron (III) nitrate, magnesium sulfate, and carbon and magnesium electrodes.

My question is:

  When the iron $3+$ ions are reduced, do they reduce to iron $2+$ ions or to solid iron?

I know the reduction potential for iron $3+$ to iron $2+$ is greater, indicating that it is more likely to occur.


texts:
I have some pieces of lead ($\ce{Pb}$) at home. I keep them in a box in the closet and never touch them.

Can it be harmful?
Should I throw them away?

I would like to keep them, but I am not certain about their toxicity.


texts: Organic compounds that react with carbonate ions

texts:
I want to remove carbonate ions from dissolved potassium carbonate (potash) by letting an organic compound react with the carbonate ions. I don't have a very good knowledge of organic chemistry, but are there certain types of organic molecules that can react with these carbonate ions to form new compounds?

Additionally, are there reactions in which the carbon atom from the carbonate ion can be inserted into the main carbon chain of another organic compound (making, for example, propane from ethane)?


texts: The distinction between graphene supercapacitors and reduced graphite oxide supercapacitors

texts:
Looking at this study, Direct laser writing of micro-supercapacitors on hydrated graphite oxide films, a consumer laser cutter is used to synthesize reduced graphite oxide supercapacitors from hydrated graphite oxide film.

In a similar study at UCLA (scalable fabrication of high-power graphene micro-supercapacitors), graphite oxide film is used again but "LightScribed" by a LightScribe DVD player to form graphene supercapacitors.

What is the distinction between reduced graphite oxide and graphene. And why are the products of laser treated graphite oxide different in these papers?


texts: Hessian Matrix and Physical directions: Potential Energy Surface

texts:
How do the eigenvectors of the Hessian Matrix for potential energy surface correspond directly to the physical directions of translation, rotation and vibration?

I see that they might correspond to some physical directions, but it seems fishy that they directly correspond to these very neat directions.


texts: How do I measure the density of a cellulose acetate membrane?

texts:
I've been playing around with filtration methods, and got my hands on a casting machine for this purpose.

My first mission was to find out how porosity can affect filtration. To see this for myself, I just ran some titratable solvent through the membrane I produced, and analyzed the difference in concentration.

Looking through some textbooks, I found a neat formula for calculating porosity, but there's one thing that's been bugging me. The formula requires the density of the membrane.

This isn't something that I can just use the Archimedes Principle to get. I need to look at the wet weight and dry weight of the membrane or whatever.

My dilemma right now is I can't find a single resource that lets me measure the density of a membrane without requiring either some pricey machine or extremely esoteric methods that's beyond my abilities. I'm really at a loss right now for this particular method.

There's this equipment here that's usable, but that looks like one high-end son of a gun. I really don't want to throw any more money than I already have.

How do I measure the density of a membrane with tools available in the home?


texts: What does the commercial chemical composition notation "Percent dry, wet with water"mean?

texts:
I am not a chemist, I develop software. I'm hoping for a general explanation I can understand in order to assist me with a project I'm working on.

Customers viewing a product online such as peroxide see 97% (dry wt.), wet with 25% water.

What does this mean? What would you expect the product to be in the form of? A powder, liquid/gel, solid in water? Any specific type of container?


texts: Fundamental vibrational modes for QM9 molecules

texts:
QM9 dataset contains about $134000$ small organic molecules with following properties computed using DFT approaches:
A = "rotational_constant_A"
B = "rotational_constant_B"
C = "rotational_constant_C"
mu = "dipole_moment"
alpha = "isotropic_polarizability"
homo = "homo"
lumo = "lumo"
gap = "gap"
r2 = "electronic_spatial_extent"
zpve = "zpve"
U0 = "energy_U0"
U = "energy_U"
H = "enthalpy_H"
G = "free_energy"
Cv = "heat_capacity"

In many papers, fundamental vibrational modes $\omega_1$ is also mentioned along with these properties. I was wondering:

Can we calculate $\omega_1$ given the properties above?
Are rotational constants used for computing $\omega_1$?
Do we need DFT calculations to compute $\omega_1$ and zero point vibrational energy (ZPVE)?


texts: Balanced equation for Schweizer's reagent production?

texts:
In Thompson's Illustrated Guide to Home Chemistry Experiments the chemical formula for Schweizer's reagent is represented as $\ce{[Cu(NH3)4](OH)2}$ (although Wikipedia represents it as $\ce{[Cu(NH3)4(H2O)2](OH)2}$ ).

Using Thompson's formula, it seems a balanced equation for producing Schweizer's reagent by disolving copper (II) hydroxide in aqueous ammonia would be:

$\ce{Cu(OH)2 (s) + 4 NH3 (aq) -> [Cu(NH3)4](OH)2 (l)}$

This indicates a ratio of 1:4 for copper hydroxide to ammonia.

Is the above balanced equation, and the indicated 1:4 ratio, correct? If not, what might be a correct representation?

(Note: This is a more specific question related to a broader question about Schweizer's reagent production.)


texts:
The usage of dialkylboron triflates produces Z enolates from ketones predominately, while the usage of dialkylboron chlorides changes the selectivity favoring the E enolate:

How is this trend explained?


texts: How do manufacturer remove oxygen from metal during melting?

texts: How do manufacturers remove oxygen from metal during melting? I melt aluminium with nichrome wires and during melting it, it forms lots of slag (aluminium oxide) and I have to remove it manually.


texts: Reaction of Copper and concentrated sulphuric acid

texts:
We know that dilute $\ce{ H2SO4}$ doesn't react with copper because copper has higher reduction potential ($0.33$) as compared to hydrogen ($0.00$).
However, it reacts with conc. $\ce{H2SO4}$ and gives $\ce{CuSO4}$ with $\ce{SO2}$ and $\ce{H2O}$.
Why does this reaction take place?


texts: Behavior of Natural Abundance and Mass Spec Ratios

texts:
The presence of sulfur in a mass spec is 96% and 4%. I believe this to be because the natural occurrence of sulfur isotopes are within these proportions.
However, chlorine behaves in a 66%/33% ratio in mass spec, but the most abundance isotopes of chlorine are 75%/25%. Why is this so?


texts: Why does lead(II) acetate does not ionize appreciably?

texts:
As this page in this book says, lead(II) acetate is soluble, but does not ionize appreciably. It seems contradictory to me, since, to call a substance soluble means it has high $K_\mathrm{sp}$ (when compared with other substances with the same elemental ratios in their formula units). But how can the book say it doesn't ionize appreciably? Why call it soluble then?

EDIT: I forgot that it is wrong to say that "to call a substance soluble means it has high $K_\mathrm{sp}$", so I revised it accordingly.

Here's the picture of the actual paragraph for those who can't access the link:

I recognize that this question actually reflects my inability to distinguish between dissociation and dissolution, now that I have cleared it from me, I rephrased the question to reflect my actual question. I did not erase the previous version to be able to show the reference of MEL Science's and alphonse's answers.

ACTUAL QUESTION: Why does lead(II) acetate not dissociate appreciably in water, considering that the ionic forms of acetate and lead(II) ion can be hydrated well due to the presence of partial charges in the water molecule?


texts:
I am looking for a way to convert XYZ coordinates into z-matrix for Gaussian input files. I need to specify certain coordinates in the matrix, therefore, the automatic built-in function from gaussview isn't of much help. Do you know of a program that can help me?
Thanks in advance for your help!


texts: Comparison of Resonance Energies of some Carbocations

texts:
We were given the following carbocations and asked to compare their resonance energies.

$\ce{L-CH2+}$, where $\ce{L}$ is:

$\ce{NH2}$
$\ce{OCH3}$
$\ce{Ph}$
$\ce{F}$
$\ce{Cl}$
$\ce{NO2}$

and the order was given as:

$1 > 2 > 3 > 5 > 4 > 6$

I am clear with the other orders but I am unsure about $\ce{F}$ and $\ce{Cl}$. Why does $\ce{Cl-CH2+}$ have a higher Resonance Energy than its $\ce{F-CH2+}$ counterpart even though in resonance, $\ce{Cl}$ forms $\ce{{3p}-{2p}}\ \pi$ bonds compared to $\ce{{2p}-{2p}}$ ones in $\ce{F-CH2+}$, which are less stable due to less efficient overlapping? $\ce{F-CH2+}$ does have a higher electronegativity, but is it enough to overcome the higher stability of the $\ce{{2p}-{2p}}$ bond over the $\ce{{3p}-{2p}}$ one?


texts: When making a calibration curve, do we have to use the wavelength at maximum absorbance?

texts: If you are making a calibration curve for $\ce{CuSO4}$ where you plot absorbance against concentration, does the wavelength have to be exactly at the maximum of the peak? Or can it be somewhere else along the curve of the peak as long as it is consistent among all the measurements and still get an accurate result?


texts: Effect of temperature and pressure on structure of solids

texts:
What is the effect of these conditions on the structure of solids? My book has the answer that confuses me. I got nothing about it. Can you please explain? The answer of the book is

  With the increase in temperature, coordination number of ion decrease. With the increase in pressure the coordination number of ions increase.


texts: Why does a silanized glass surface become hydrophobic?

texts: What is the physical reason that a glass surface becomes hydrophobic by silanization? (e.g. is it due to increase in surface roughness due to the long chains which is created on the glass surface? or ...)


texts:
I would like to know if a Mulliken population analysis to calculate spin densities is in general a valid choice. I see that it is made use of, for example here1.  So up to-date researches apparently use it. On the other hand there seem to be more advanced methods (natural population analysis). Moreover Wikipedia states:

In principle, a complete basis set for a molecule can be spanned by
placing a large set of functions on a single atom. In the Mulliken
scheme, all the electrons would then be assigned to this atom.

So there is some ill definition for this method. This would not only account for charge analysis but also spin, if I am not mistaken.
Knowing that my basis set is reasonable; is there anything to consider that would make Mulliken spin density analysis doubtful?
References

H-Bonding on spin centres enhances spin–spin coupling for organic diradicals by Francis Kirby B. Burnea,  Yeonsig Nama  and  Jin Yong Lee, Journal of Materials Chemistry C, Issue 10, 2020 (link)


texts:
$\ce{Fe^3+ + e- -> Fe^2+} \quad +0.77$
$\ce{Fe^3+ + 3e- -> Fe} \quad -0.04$
$\ce{Fe^2+ + 2e- -> Fe} \quad -0.41$
$\ce{Zn^2+ + 2e- -> Zn} \quad -0.76$
$\ce{Co^2+ + 2e- -> Co} \quad -0.29$
$\ce{Ni^2+ + 2e- -> Ni} \quad -0.25$

I am having a hard time to understand if there is a trend in reduction potentials so predictions could be made on whether a certain 'strong' (e.g. $\ce{NaBH4}$) or 'weak' (e.g. hydrogen) reductant  reduces an iron salt. I also wonder if there is a trend in the periodic table between first row d metals.

My question is possibly best split into two: Is there a trend in the periodic table regarding reduction potentials? Why is iron (our of the first row elements) so hard to reduce compared to others?


texts: Where does the energy of solar radiation hitting the atmosphere go?

texts: I was reading about solar radiation, and there was a part that says that the atmosphere absorbs most of the radiation emitted by the sun. I wonder if when the atmosphere absorbs the energy, where does it go since energy doesn't disappear or that's what I've been taught in high school. I'm guessing it transforms to heat. Correct me if I'm wrong, and a explanation would be very appreciated.


texts: Why is oxalic acid more acidic than benzoic acid?

texts:
I came across this fact while reading my book and was confused. Looking at the structures, I had the intuition that benzoic acid would be more acidic as the conjugate base formed will resonate all over the benzene ring.
Why does this happen?


texts: Why Gibbs energy change of a process can be negative at constant temperature and pressure?

texts:
This question has been asked before, but the answers are not clear and satisfactory.
If the pressure and the temperature are constant then G would be always zero. How would then G have a value other than 0?


texts: Experiment using hydroxides of alkaline earth metals

texts:
In three different test tubes we add a very small amount of:

1)In the first test tube, we add oxide of magnesium

2)In the second test tube, we add hydroxide of calcium

3)In the third test tube, we add hydroxide of barium

Then we add deionized water in the three test tubes. We shake them and after we filtrate them, we measure the pH of each filtrate.
I'm curious why we use hydroxides of calcium and barium but we use oxide of magnesium instead of hydroxide of magnesium?


texts: Which reaction is useful to prepare odd number of hydrocarbons?

texts:
Which reaction is useful to prepare odd number of hydrocarbons:

Wurtz reaction
Kolbe electrolysis
Corey–House synthesis
Oxymercuration

Wurtz reaction produces even products except if we take mixtures. Kolbe ones give even ones too. Oxymercuration merely involves addition, so I think it's Corey–House.

But how does one justify that exactly? Is it because of $\ce{Cu(CH3)2Li}?$


texts: What does the letter R represent in chemical structures?

texts:
The letter $\ce{R}$ appears frequently in chemical structure illustrations. For instance, when I Google keratin, I find Wikipedia's Spanish article about it.

In the image illustrating part of the chemical structure, I see elements like $\ce{H, C, O, N, and S}$ - which I recognize - but I also see $\ce{R}$, which I do not. What does $\ce{R}$ stand for in this context?


texts: Intermolecular and Intramolecular Forces (Vapor pressure of n-butylamine and methanol)

texts:
What are the different properties that intermolecular forces and Intramolecular forces attribute to? i.e. intermolecular forces contribute to BPs, vapor pressures, etc.

Specific problem: why does n-butylamine have lower vapor pressure at room temperature than methanol? Explain in regards to IMFs.


texts: Corrosion of metals and observations in the agar medium?

texts:
I want to know which metals oxidize and which is reduced and changes in medium and observations?

According to my knowledge more corrosion will take place in Zn and Fe also corrode. Then copper should reduce. So, for both reactions, will copper acts as the cathode?
I need general but complete explanation. Thank you


texts: Does Acetate Cause Major E2 On Tertiary Haloalkanes?

texts: This question really confuses me. I've narrowed it down to E2 being favored in step one (giving 2-methylpropene), but I don't see how a relatively weak base like acetate could cause E2 to be the major product. The only other explanation I could think of is that E2 is a substantial minority product, so the reaction isn't synthetically useful. Am I on the right track? Thanks!


texts: How does overvoltage affect the products of electrolysis?

texts:
When you electrolyse an aqueous solution of $\ce{NaCl},$ the product formed at cathode is $\ce{H2}$ gas (preferential discharging), but the product formed at anode is $\ce{Cl2}$ gas. According to standard electrode potential, reduction of $\ce{Cl2}$ is 1.36 V and $\ce{O2}$ is 1.23 V.

Keeping the values in mind, $\ce{O2}$ gas should be formed at anode because it has a smaller electrode potential. But it is given that chloride ions is preferred by anode because of a phenomena called overvoltage.

I don't understand how overvoltage can effect the products of electrolysis.