texts: Hydrogen peroxide and potassium iodide reactions

texts:
What is the explanation for the two possible reactions of $\ce{H2O2}$ with $\ce{KI}$ in acid media (iodide-catalyzed decomposition of hydrogen peroxide or iodide oxidation by hydrogen peroxide) and what determines the prevalence of one over the other?
It is known that if the hydrogen peroxide is concentrated, the pathway which results in the decomposition of hydrogen peroxide is favored. Otherwise, the iodide oxidation is predominant.
Two well-known chemistry demonstrations (elephant's toothpaste and the iodine clock) rely on these reactions.
The first one involves the decomposition of hydrogen peroxide
$$
\ce{2H2O2 ->[\ce{KI}] 2H2O + O2}
$$
which is believed to occur through the following mechanism
$$
\ce{H2O2 +I- + H+ -> HOI + H2O}
$$
$$
\ce{HOI + H2O2 -> H2O + O2  +I- + H+} \text{(rate-determining step)}
$$
On the other hand, the reaction that happens in the iodine clock is
$$
\ce{H2O2 + 3 I- + 2 H+ -> I3- + 2H2O}
$$
I would like to understand this phenomenon based on thermodynamic or kinetic data, since I could not find an explanation for it.


texts: How to calculate spectral overlap integral using spreadsheets?

texts:
I need to calculate the spectral overlap integral for the emission spectrum of coumarin 334 and the absorption spectrum for rhodamine, using spreadsheets (MS Excel).

Following the theory of Fluorescence Resonance Energy Transfer (Förster), I have the definition of the spectral overlap integral:

$$
J(\lambda) = \frac{\int_{0}^{\infty}f_\ce{D}(\lambda) \epsilon_\ce{A}(\lambda) \lambda^4\,\mathrm{d}\lambda}{\int_{0}^{\infty}f_\ce{D}(\lambda) \,\mathrm{d}\lambda}
$$

I also have the data for emission spectrum of the donor (coumarin 334) and the absorption spectrum of the acceptor (rhodamine). However, I am not sure how to proceed and actually extract the spectral overlap. Since the spectral overlap is a function of wavelength, will I end up with a "spectral overlap spectrum"? And how do I get the absorption coefficient of rhodamine? I have been given the maximum absorption coefficient (at wavelength of maximum absorption), but how do I get the molar absorption spectrum, $\epsilon_\ce{A}(\lambda)$?

Should I calculate values at a "per-wavelength" basis, or should I fit functions and integrate those?


texts: What are the resonance structures of 3-aminocyclohex-2-en-1-ylium?

texts:
How would you draw the resonance structure for the compound below:

This is one of the resonance forms I think... but I'm sure there is another one too.


texts: Mechanism of homologation of aldehyde to alkyne: Ohira–Bestmann reaction

texts:
This reaction was part of an organic scheme I was doing, and I was wondering what the mechanism of the reaction would be.

I tried first forming a carbene by letting $\ce{N2}$ leave from the diazocarbonyl. Then, I did a Wolff rearrangement, attacked the ketene with water, decarboxylated the COOH, then did a Wittig reaction with the phosphonate ester. However, I ended up with an alkene and not the alkyne.
I also tried first doing the Wittig rxn, but I didn't know where to go after that (since you can't form the carbene anymore).
Any help with the mechanism of this reaction would be appreciated.


texts: Flexible & thermally conductive materials?

texts: Quick question: Are there any common or easily obtainable materials that are thermal conductors, but also flexible? By flexible, I mean along the lines of a plastic bag, with similar or greater durability.


texts: Comparing Methods of Determination of Dissolved Oxygen Content in Water Sample

texts:
I am currently doing an IB Chemistry Individual Investigation on dissolved oxygen in water samples by using Winkler method. However, my teacher suggested that I have to use oxygen probe as a standard and comparing the efficiency of dissolved oxygen content determination between Winkler method and other methods.

My problem is I don't know what method I have to compare with the Winkler method that I had done. Are there any suggestions or improvements on my investigation to let it have more exploration aspect?


texts: Does DCl have a higher rotational partition function (qrot) than HCl? And if so why?

texts: I know that DCl has a higher moment of inertia than HCl, but I can't really explain how this actually affects the rotational partition function, I know larger molecules have a higher moment of inertia and this means the energy levels are closer, but I don't know how to explain how this has an effect on the partition function of rotation, can someone help?


texts: Gel filtration separation of cellulose, starch, oxytocin and palmitic acid

texts:
I am studying biochemistry and I have been asked by my teacher to find a procedure for separating cellulose, starch, the peptide oxytocin (9 a.a) and palmitic acid ($\ce{C16}$) using gel filtration chromatography. I have some ideas about using Fehling's test to tell the cellulose from the starch and the peptide since they all react with the $\ce{Cu^{2+}}$ in the solution. And I'm thinking that the palmitic acid will not dissolve in the solution and can therefore be separated from the others.

However, I have a problem with how the gel filtration would work. Obviously cellulose and starch are much bigger than palmitic acid and oxytocin but, how could I possibly separate cellulose from starch using gel filtration??

Gel filtration: https://en.wikipedia.org/wiki/Size-exclusion_chromatography


texts: Solvent for recrystallization of benzoic acid?

texts:
Which is best solvent for recrystallization of benzoic acid?

Water
$\ce{CH3Cl}$
$\ce{CCl3COOH}$
$\pu{0.1 M}\ \ce{NaOH}$

I understand the solute/solvent should be soluble at high temperature, and insoluble at room temperature. But how to make the specific arguments for eliminating the alternatives?


texts: The significance of the dissociation constant of an indicator

texts:
In the chapter acid-base, I learned about indicators and how they are actually weak acids.

This is the equation given in our book:

$\ce{HIn + H_2O <=> H_3O^+ + In^-}$

$K_{in}= \left(\frac{[\ce{H_3O^+} ][\ce{In^-}]}{[\ce{HIn}]}\right)$

When $\ce{HIn}$ and $\ce{In^-}$ are of different colors

My question:

Further in my book, the concentration of $\ce{H_3O^+}$ at which $\ce{[HIn]=[In^{-}]}$ is calculated. Apparently, this is the concentration of $\ce{H_3O^+}$ at which the indicator changes color and thus this can be used to identify end point of a titration. However, how is this the point where the indicator "changes" color, I mean isn't the indicator changing color throughout the titration as the concentration of $\ce{H_3O^+}$ is changing continuously as the alkali is added to the acid for example
Why do different indicators have different $pK_{in}$ i.e. "change color" at different concentration of $\ce{H_3O^+}$


texts: In Chemistry, is it possible to use the old representation of the atom as a nucleus surrounded by orbiting particles?

texts:
In Physics, Newton's laws are enough for many applications. Sometimes, relativity must be used instead or complementary, and sometimes, Quantum Mechanics.

Is this the same case with Chemistry? Are there areas of Chemistry where the simplification of electrons as little particles orbiting the nucleus at distances proportional to their energy level is possible? Or does all of modern Chemistry must use Quantum Mechanics? At what point Chemistry "breaks" if the particles and orbits model is used?


texts: Does anybody have any ideas about the trend that I found for luminol chemiluminescence reaction? Or can anybody help me analyze them?

texts:
The reaction that I did is shown below. I'm testing the duration and luminosity of the light the reaction produces against different pH. The way I used to control the pH is by adding more or less $\ce{Na2CO3}$ since it is basic with a pH of 11.
Solution A: In $\pu{200 ml}$ water, add in $\pu{0.16 g}$ $\ce{Na2CO3}$, $\pu{0.04 g}$ luminol, $\pu{5 g}$ $\ce{NaHCO3}$, $\pu{4.6 g}$ $\ce{(NH4)2CO3}$, and $\pu{0.08 g}$ $\ce{CuSO4}$.
Solution B: In $\pu{200 ml}$ water, add in $\pu{10 ml}$ $\ce{H2O2}$
Then, pouring $\pu{50 ml}$ of solution B into $\pu{50 ml}$ of solution A, a bright light will be produced. The light will gradually fade away but the light will be produced again after some time, a guaranteed second reaction for every trial. (Could someone also tell me how could this happen?)
The trend that I found is shown below:


texts:
From the rules I know I would name the following compound as 3-propyl-penta-1,3-diene because maximum number of functional groups (double bonds in this case) are in the five numbered carbon chain:

However, ChemDraw names the above compound as 3-ethylidene-hex-1-ene. Why? Am I missing a rule?


texts: Microorganism preventative solution safe for using on a roof and will last in the sun

texts: Information is scarce in the roof cleaning industry and the big guys are making a killing selling chemicals that are harmful to the person using it and everything around the home. I would like to find something safe that I can use to prevent microorganisms from ever popping back up on my customers roofs.


texts: How do I calculate the mass percent in the original mixture?

texts:
I have the question:

  "A mixture of $\ce{KClO3}$ and $\ce{KCl}$ with a mass of 0.950g was heated to produce $\ce{O2}$. After heating, the mass of residue was 0.700g. Assuming all the $\ce{KClO3}$ decomposed to $\ce{KCl}$ and $\ce{O2}$, calculate the mass percent of $\ce{KClO3}$ in the original mixture."

I took the amount of $\ce{O2}$, converted it to moles $\ce{O2}$, then divided it to moles of just O, then divived by 3, bcause for every 3 O (for the 3 in the $\ce{KClO3}$) there is a mole of $\ce{KClO3}$ so I had moles of $\ce{KClO3}$. Then I converted that to grams of $\ce{KClO3}$, but thaat ended up as more then the original mixture's mass.

Am I even thinking about this the right way?


texts: Does the activity product decrease with increasing ionic strength?

texts:
I have a question regarding what happens to the solubility of $\ce{CaSO_4}$  or the rate that $\ce{CaSO_4}$ will dissolve when we add $\ce{NaCl}$ to the solution:

$\ce{CaSO_4}$ will dissolve into $\ce{Ca^{2+}}$ and $\ce{SO_4^{2+}}$:

$$\ce{CaSO_4$ $<=>$ $Ca^{2+}$+$SO_4^{2+}}$$

The ionic strength has the expression:

$$I = \frac{1}{2} \sum (m_i z_i^2)$$

where $m_i$ is the molar concentration of species $i$, and $z_i$ is the charge of species $i$.

If we add $\ce{NaCl}$ to the solution, it follows that we get more ions, and therefore the ionic strength will increase.

The expression for activity coefficients for ionic strength up to about 0.5 is:

$$\log\gamma_{i} = -A z_{i}^{2} \left({\sqrt{I}\over 1 + \sqrt{I}}\right) - 0.3 I$$

where $A$ is a constant, $\gamma_{i}$ is the activity coefficient for species $i$, and $I$ is the ionic strength. If I then use $A = 0.5$, I get:

$\gamma_{Ca_{2+}}$=0.296 at $I=0.5$

$\gamma_{Ca_{2+}}$=0.291 at $I=0.4$

$\gamma_{Ca_{2+}}$=0.297 at $I=0.3$

$\gamma_{Ca_{2+}}$=0.318 at $I=0.2$

Since we increase the ionic strength by adding $\ce{NaCl}$, is it correct that the activity product of calcium and sulfate would decrease (even though I did not get that in the above calculations), and that because of this calcium sulfate would dissolve more?


texts: What really is an equation of state (EOS) and how are they developed?

texts: Are EOSs merely correlations that mathematically represent (in a better or worse way) experimental data or do they have a theoretical background? How are they developed (suppose one wishes to develop his/her own EOS -- how would he/she start and which script should he/she follow?).


texts: Deriving a reduction potential from two other reduction potentials

texts:
Given:

  \begin{align}
\ce{Co^{3+}(aq) + e-  &-> Co^{2+}(aq)} &   E° &= \pu{+1.82 V} \\
\ce{Co^{2+}(aq) + 2e- &->  Co(s)}      &   E° &= \pu{-0.28 V}
\end{align}

  what is the standard reduction potential for $\ce{Co^{3+}(aq) +3e-  -> Co(s)}$?

If I add up these two half-equations to get the desired half-equation, I get $E^\circ = \pu{+1.54 V}$. But the correct answer is $\pu{+ 0.42 V}$!

Am I missing something?


texts: What is the correct number of stereo isomers in case of 3,6-dimethylpiperazine-2,5-dione?

texts:
What is the correct number of stereo isomers in case of the following compound, i.e. 3,6-dimethylpiperazine-2,5-dione?

The answer key gives three, but I think there should be four.
I recognised the two planes of symmetry, one through the methyl groups and the other through the keto groups.


texts:
On p. 429, when introducing the idea of bromonium ions, Clayden et. al.[1] mention that:

  You can think of the bromonium ion as a carbocation that has been stabilised by interaction with a nearby bromine atom. You have seen a similar effect - this 'oxonium ion' was an intermediate, for example, in the $\ce {S_N1}$ substitution of MOM chloride on p. 338 of Chapter 15.

This carbocation stabilisation described in the text above is illustrated in the image below. The case described seems to be that of an adjacent carbon with a positive charge. However, I was wondering if a carbon one atom away with a positive charge could be stabilised in the same manner as well. This would be more similar to the bromonium ion. I have illustrated what I am referring to in the image below.

I would like to ask if this "interesting oxonium ion", as an oxygen analogue of the bromonium ion, does exist in reactions, such as $\ce {S_N1}$ substitutions.

Reference:

Clayden, J.; Greeves, N.; Warren, S. Organic Chemistry, 2nd ed.; Oxford UP: Oxford, U.K., 2012.


texts: If aliens lived in a hydrogen (or any flammable gas) based atmosphere, would they perceive oxygen to be flammable?

texts: Energy, fuel, and oxygen are needed for a fire to burn. In a hydrogen chamber, if there was a pipe spewing small amounts of oxygen, could you light the oxygen on fire as it began to mix with the hydrogen?


texts:
Please help me clarify the title if you come up with a better way to put it (you certainly will).
My question is the following:
If you make a mix of equal parts of various acids (Bicarbonate, Hydrochloric, Nitric, Sulfuric, etc.) and throw some metal in there that will ionize and wait for a while until you have an equilibrium, what will that resulting equilibrium look like vs. the known solubilities of the expected salts? Where and in what form will the metal ions most likely end up? Will the metal's solubility tend towards an average of the expected solubilities? Or tend towards the solubility of the least soluble metal salt? Or of the most soluble metal salt? Or exceed the solubility of the most soluble salt?
This is assuming that no acid is / would have been limiting in reacting with the metal in the first place.
My assumption is that most metal ions would end up precipitating as the least soluble salt but I'm very much unsure of myself.
Upon Poutnik's advice, here are two examples I provided in the comments:
Case No 1: I drop 1 mole Cadmium metal in a solution with 5 moles of sulfuric acid and a great excess of water beyond the solubility limit of the product (I assume it would dissolve entirely), I then add 5 moles of phosphoric acid. Would that (a) precipitate most of the nickel (almost as if only phosphoric acid was present), or will (b) the solubility be somewhere between that of the sulfate and phosphate salts, or (c) most of the nickel remain in solution as if only the sulfate was present?
Case No 2: I drop 1 mole of lithium and 1 mole of cadmium metal into 2 moles of sulfuric acid with enough water for both to be entirely dissolved. I then add one mole of phosphoric acid, leave the solution in a sealed container with heavy stirring and come back 1000 years later. I then filter out and analyze the precipitate: Will it be all cadmium / mainly cadmium / an even mix of both cadmium and lithium phosphate salt? (knowing both cadmium and lithium form insoluble phosphate salts, but the solubility of the lithium salt is several orders of magnitude above that of the cadmium salt). Let's assume there is no double salt formed for the sake of simplicity.


texts: Role of zinc chloride in reaction of ether

texts:
I am trying to do a reaction between acetyl chloride $\ce{CH3COCl}$ with diethyl ether. I know that upon using anhydrous $\ce{ZnCl2}$ and heat, I'll get an ester and an alkyl chloride, but I'm not able to guess the mechanism.

Does $\ce{ZnCl2}$ break the $\ce{C-O}$ bond in ether as it would've done to alcohol? Please help me with the mechanism.


texts: Is this analogy explaining the difference between enantiomers and diastereomers correct?

texts:
I tried writing an analogy to explain the difference between enantiomers and diastereomers. However, I'm not entirely sure if it's actually a correct representation of the differences. It might also be more confusing than it has to be:

To use an everyday object as an illustration of the difference, imagine two forks with four tines each. If fork 1 has its first and third tine longer than the other ones, and fork 2 has its second and fourth tine longer than the other ones, then the two forks would not match completely if you tried to stack them on top of each other. However, if you held fork 2 up to a mirror, then you would see it now has both its elongated tines in the same place as fork 1. These forks would be enantiomers of each other because they are the same thing, but mirror images of each other
If you changed fork 2 to have its first and second tine longer than the other ones, instead of the second and the fourth, then the two forks would instead be diastereomers. This is because now they both cannot match completely when stacked on top of each other, and holding either one up to a mirror will not make them look any more similar. This is exactly how diastereomers work too, because it only partially mirrors its counterpart. As you can see, fork 2 now has its first elongated tine actually match the first elongated tine of fork 1, while also retaining the effect that holding it up to a mirror will have its second elongated tine match that of fork 1. That is, in the mirror fork 2 will have its third tine elongated, just like fork 1 does when not viewed through a mirror. In other words, fork 2 has its first elongated tine match fork 1’s, but its second elongated tine is the mirror image of fork 1’s. This makes them diastereomers because they are the same thing, but neither structurally identical nor complete mirror images of each other.

So, is there anything off about my analogy, or does it correctly and comprehensibly explain the difference between the two?


texts: Velocity of electrons ejected from Cl atom

texts:
When neutral $\ce{Cl}$ atoms are bombarded by high energy photons, causing ejection of electrons, which subshells' ejected electrons will have highest velocity?

I chose $1s$ because I thought more energy is needed to ejected those electrons so they might have higher velocity. My second choice $3s$ is right, but I can't explain why.


texts: Can fluorescent & phosphorescent molecules still be fluorescent or phosphorescent as ions and not as salts?

texts:
The way my pchem professor explained it is that fluorescence /phosphorescence is caused by collision excitation. During this collision the spin of the promoted electron is flipped to a parallel spin of the orbit it left. The Pauli Exclusion Principle prevents relaxation/emission until the electron is some how able to "flip" its spin.

Most of the phosphorescent compounds I've found online have been salts which makes a bit of sense, (I imagine that the oscillation of the ionic bond is what causes the collision excitation). However, not all of them are salts. In lab previously our solution of sodium fluorescein exhibited a small degree of phosphorescence even when in basic conditions. I'm curious how a molecule can promote to a triplet spin multiplicity internally.

My professor says that the ionic component is not necessary and these compounds are typically ionic for the purpose of stability and longevity.

If the ionic bond isn't contributing to the triplet spin multiplicity then what is causing it?


texts: About the Vilsmeier-Haack formylation of this compound

texts:
I was reading an article and found the following reaction sequence:

The second step involves a formylation of the hydrazone with the Vilsmeier reagent to, first synthesize the pyrazole ring and then, to formylate it to produce the final compound. However, when reviewing this reaction I found many examples in which it is used to formylate phenols and other electron-rich arenes. My question is why doesn't the formylation occur on the phenol of the example?
I'd appreciate if someone could provide an answer.


texts: What will be the final product when the above bridged compound is heated with concentrated sulfuric acid?

texts:
What will be the final product when the above compound ((1S,2S,4R,7S)-7-methylbicyclo[2.2.1]heptane-2,7-diol) is heated with concentrated sulfuric acid?

I know that the hydroxyl group in the bridgehead position cannot be protonated and removed to form a carbocation. The other hydroxyl group may be protonated and removed to form a carbocation I suppose. But after that what rearrangements will take place ? What will be the final product(s)?


texts:
The entropy is defined as randomness of a substance or a system.
The randomness increases as we go from solids to liquids to gases. Similarly from hard diamond to soft graphite. Since graphite is soft and slippery, the orderness would be less than diamond.

But acc. to the formula for entropy change during phase transition,
$\Delta S=Q\ \text{(at const. pressure)}/T$
$\Delta S=\Delta H/T\ \text{(at const. pressure)}$

But $\Delta H$ of reaction/process
C graphite --> C diamond is positive
Meaning $\Delta S$ is positive. But it should be negative due to less entropy of diamond.

Where is the problem?


texts:
I am a physics student trying to calculate some values for a project I am working on, and am confused about Henry's constant.

I want to dissolve certain noble gases into freon in a pressurized chamber with temperature control, and want to know some of the numbers ahead of time.

I have seen the equation for the constant: $$K=\dfrac{p}{c}$$

My question is this: Where do the solvent characteristics come into play? I don't see how using this constant equation would get me a different constant for say, argon, in water vs. $\ce{C3F8}$?


texts: Why can we not use water instead of blank control solution in enzyme catalysis with Peroxidase experiment?

texts: I have to do a lab about enzyme catalysis with peroxidase in my chemistry class. We are to use the blank control solution in the experiment. My question is, why can we not use water instead? I did some research about this and someone says something like "It is because the water blank absorbs so much light that the usable scale is compressed, thus, causing a poor accuracy." Is this the exact reason why we do not use water in this experiment?


texts: Examples of application of surface area maximization to crystallography or molecular geometry

texts: Suppose that N points are chosen from the unit ball (or its boundary, the sphere) in three-dimensional space R^3. Consider the convex hull of these N points (assume N is at least 4). The resulting object is a polyhedron inscribed in the sphere. Now consider the problem of maximizing the volume (or surface area) of this convex hull. Does such a problem have any applications to crystallography or molecular geometry?


texts: Why does the corrosion of a steel nail develop iron ions in the ends of the nail and hydroxide in the middle of the nail?

texts:
We did an experiment in school where we put a steel nail in a solution consisting of:

1 g agar;
100 ml water;
100 ml indicator solution (which gets blue whenever $\ce{Fe^2+}$ is created and red when $\ce{OH-}$ develops).

We let it rest for a few days and this is what happened to the nail:

My hypothesis was that the corrosion would create two ends of the nail where reduction takes place in one end and oxidation on the other end. Why isn't this the case?

My teacher gave us a hint and told us it could have something to do with both:

The length of the nail;
The ion concentration of solution.


texts: Which affects acidity more, in relation to induction? (Distance vs. quantity)

texts:
I already know that the answer is III. I'm just looking for further explanation on how the others compare to each other, mainly IV vs V.
I know that iodine is less electronegative than chlorine, making I the least acidic.
Only having one chlorine atom, while the rest have two, puts II next in line.
III is the most acidic, due to the two chlorine atoms being on the same carbon, and closest to the sulfur group.

My question comes in for the comparison of IV and V. While V has two chlorine atoms on the same carbon, they are both 3 carbons away from the sulfur group. Meanwhile, IV has one chlorine atom closer to the sulfur group, but the other isn't on the same carbon atom.
Which one of these is more effected by induction? Proximity to the sulfur group (IV) or being grouped together on a single carbon (V)?


texts: Why do some chemical reactions require many steps?

texts:
I posted the following question in Physics SE and was advised to transfer it to Chemistry SE.

I studied physics in college ten years ago and I recently started to learn biochemistry. I enjoy finding out that some familiar concepts in physics play important roles in biochemistry such as entropy and the Gibbs free energy.

For example, as a (ex-)student of physics, I am happy to know that the Gibbs free energy determines the directions of chemical reactions. I feel this is a good example where a sort of fundamental law of physics determines how a phenomenon looks like.

However, I still can not understand why the chemical reactions in a body need to be so complex. Many chemical systems consist of more than several steps to achieve their purposes. According to Wikipedia, glycolysis takes ten steps through its process. Why are so many steps necessary?

I tried to find out a physical law that prohibit the glycolysis process from being achieved in one or two steps, but I could not find an answer. I would like to know (or discuss) whether there is a physical law that makes chemical systems so complex (many steps required).

My assumption is that some physical law prohibit the existence of an enzyme that realizes a one-step process of glycolysis.


texts: Peptide bond formation involving side chains of charged amino acids

texts:
Peptide bonds are formed as such:

Aspartic acid, glutamic acid and lysine all contain either one extra $\ce{-COOH}$ or $\ce{-NH2}$ group in them. Why does that extra group not participate in peptide bond formation? For reference, the structure are given below:

It should be possible for the $\ce{-COOH}$ group attached to $\ce{C}$3 in aspartic acid and $\ce{C}$4 in Glutamic acid to form a peptide bond with $\ce{-NH2}$ of another amino acid. Do these bonds occur in any peptide linkage? If they do, what is the nomenclature associated with them and how do their chemical properties differ?


texts: Why is the nucleophilic substitution of OH- with 1-bromopentane slower than with 2-bromo-2-methylbutane?

texts:
Which statement about the reaction of a hydroxide ion with the organic reagent is correct?
A. 1-bromopentane predominantly follows an $\mathrm{S_N1}$ mechanism.
B. 2-bromo-2-methylbutane predominantly follows an $\mathrm{S_N2}$ mechanism.
C. Reaction with 1-bromopentane occurs at a slower rate than with 1-chloropentane.
D. Reaction with 1-bromopentane occurs at a slower rate than with 2-bromo-2-methylbutane.

I got the answer correct (D), but only by eliminating the other three options. However, why is D true? Does this mean that $\mathrm{S_N1}$ reactions are always faster than $\mathrm{S_N2}$ reactions when they are reacting with the same nucleophile?
I'd really appreciate some help.


texts: Should the liquid be included in Kc expression?

texts:
Should the concentration of liquid water be included in the $K_\mathrm{c}$ expression for the reaction
$$\ce{2 NO2_{(g)} + 7 H2_{(g)} -> 2 NH3_{(g)} + 4 H2O_{(l)}}$$
if water is liquid and all the other compounds are gasses?


texts: store alcohol tinctured herbs in polypropylene for extended time

texts: Can I store alcohol tinctured medicinal herbs in the 2 oz. food grade polypropylene cups  (PP 5) for about a week?  I would like to have several "doses" ready to go because they are taken several times a day, and I would like to have several days ready to use at all times.  Thanks


texts: How can you have a reduction potential for a non redox reaction?

texts:
The standard reduction potential for the half cell $$\ce{FeCO3_{(s)} + 2e- <=> Fe_{(s)} + CO3^2-} \quad\quad(E^o =-0.756 \text{V})$$ and the standard reduction potential for the half cell $$\ce{Fe^2+ + 2e- <=> Fe_{(s)}}\quad\quad\quad\quad\quad\quad (E^o = -0.44 \text{V})$$ are as given.

From these, I calculated the $\ce{E^o}$ for the reaction $$\ce{FeCO3_{(s)} <=> Fe^2+ + CO3^2-}\quad\quad(E^o = -0.31 \text{V})$$ How do I interpret this number because the dissolution is not a redox reaction? How do I calculate $\Delta G^o$ for the reaction since $n = 0$ in the dissolution reaction ($\Delta G^o=-R*T*\text{ln}(K)$ will not work)?


texts: Molecular orbital theory and the conservation of molecular orbitals

texts:
I am not clear with the molecular orbital theory. I have read:

  If the atomic orbitals are combined with the same phase they interfere constructively and a bonding orbital is formed.
  If the atomic orbitals are combined with different phases, they interfere destructively and an anti-bonding molecular orbital is formed.

So as per my understanding when two s-orbitals are combined either a bonding orbital can be formed or an anti-bonding orbital can be formed depending upon the type of interference.
This contradicts the following statement:

  When two atomic orbitals combine they form two new molecular orbitals.

This means that when two s-orbitals combine they produce both bonding and anti-bonding orbitals. Where have I gone wrong?


texts: Why does sensitivity of nmr spectrum improve with increased magnetic field strength

texts: I am struggling to find an equation that illustrates this and a qualitative explanation to go along with it. I presume that the noise remains at the same intensity and somehow the intensity of the genuine signal increases in intensity thus improving the signal to noise ratio.


texts: Light sensitive AgF decomposition reaction

texts:
Silver compounds such as silver fluoride are light sensitive (as are all other silver halides) so they will decompose when exposed to light.

I'm stuck with a problem : I want to expose silver(I)fluoride to light to then produce elemental silver and fluorine gas - I'm worried that because of the high reactivity of fluorine silver(I)fluoride will be formed again...

So how could I successfully split silver(I)fluoride by light into elemental silver and fluorine gas without the fluorine reacting again with the silver?


texts: Chemiluminescence - Determining Temperature from Luminol Imaging

texts:
I'm working on an imaging project and I have no background in chemistry or chemiluminescence for that matter. This is a Computer Science project.

While most of the details for it have been worked out, I'm having difficulty figuring out the scope and possibility of an important requirement.

Given a luminol image, I will develop a heat-map. For now the heat map is built based upon the intensity of the light.

However, given the intensity of the light and with the knowledge that luminol is being used, is it possible to determine the approximate temperature of the point based on its intensity and the intensity of the surrounding region?

I would assume that this chemical would burn differently at various temperature and would have a specific signature of light emitted depending on it its temperature but I'm having difficulty pinpointing whether this is true, possible and backed by research (or science).

The closest parallel I've found is combustion analysis. The heat release rate is calculated by measuring the amount of light radiated from a flame at various wavelengths, since certain chemicals give off radiations at specific wavelengths.

Can anyone confirm this, suggest alternatives or point me int the right direction?


texts: Software for visualization of 3D models of chemical structures with atomic orbitals

texts:
A number of programs are available that let you build, visualize, and analyze 3D models of chemical structures (I use Chem3D/ChemBio3D). Current versions usually include various possibilities for the calculation and graphical representation of molecular orbitals.

However, the resulting images can be overloaded or unclear. Introductory explanations using such images might be overdoing it. Therefore, many textbooks on organic chemistry use simple chemical structure diagrams based on atomic orbitals.

In particular for didactic purposes, I am looking for an intermediate solution. I would like to build, optimize, and visualize a 3D model of a chemical structure and show a graphical representation of the original atomic orbitals in the 3D model. Unfortunately, this option doesn’t seem to be available in Chem3D/ChemBio3D. Does any software exist that lets you build a 3D model of a chemical structure and visualize atomic orbitals?


texts: If Alkynes can be reduced to Alkenes using Sodium in liquid ammonia, why can't Alkenes be reduced to Alkanes?

texts: Firstly, I would like to ask why the alkyne reacts at all with the solvated electron? Surely the alkyne group is extremely nucleophilic (more so than the alkene). This, to me, seems to suggest that an alkene would be more likely to react in this manner than the alkyne. However, this is clearly not the case; why?


texts: How to get anhydrous triflic acid from triflic anhydride?

texts:
I require a small amount of triflic acid, and while other research groups do not have any, I did locate some trflic anhydride. Does anyone have a published protocol for obtaining the anhydrous acid from the anhydride?

I tried to distill under a slow stream of nitrogen about 10 mL of triflic anhydride (yellow/brown solution) with about 5 mL of DI H2O. I got a clear colorless fraction coming off with B.P. 66 C, and afterwards a second fraction with a slightly lower boiling point. The boiling point of the free acid is 162C, the anhydride is 82 C, and there is a monohydrate of the free acid with a melting point of 34 C, but I couldn't find the boiling point.

I did not find an entry in Perrin & Armarego Purification 3rd edition, or in my Fieser and Fieser.

I'll run 19F NMR on the 2 distilled fractions I got, but as the BP was so low, I expect not to get the free acid.


texts: Decreasing magnitude of peaks in cyclic voltammogram?

texts:
I'm in an instrumentation course and we covered cyclic voltammetry earlier in the semester and will be doing an experiment in CV next week.

My question is this:

If you have a reaction and sweep the potential, will the new peaks be entirely within the previous peak? (Meaning: lower magnitude in the subsequent peaks?) It seems that with each sweep, it should have lower electrical potential.

Or would the peaks trace over the previous ones, nicely?

Pardon me for not fully understanding (or if my question is wrong.)

Enjoy a poorly drawn image of what I mean:


texts: Difference in reactivity between As and Sb

texts: I know that the Marsh test can detect both As and Sb. In literature, I have found that to distinguish the elements, one can use hypochloride solutions. In fact, arsenic is oxidized to arsenic (III). But why hypochloride can not oxidize Sb?


texts: How to draw Xenon Hexafluoride in Rdkit from SMILES

texts:
So in SMILES I would think that XeF6 would be FXe(F)(F)(F)F or FXe(F)(F)(F)(F). A quick wikipedia search showed that the first result is the correct SMILES string. However, rdkit isn't able to convert either SMILES strings into a structure.
Here is my code:
from IPython.display import SVG
from rdkit import Chem
from rdkit.Chem import rdDepictor
from rdkit.Chem.Draw import rdMolDraw2D
# Create mol object from smiles string
# mol = Chem.MolFromSmiles('[B](C7OC7)(CCC3CCCC31N2CN([P]5CCCC8C5)C2(CO8)CC1)(C6CCC6)')
# The above molecule was me learning SMILES, below is the Xenon Hexafluoride string
mol = Chem.MolFromSmiles('F[Xe](F)(F)(F)(F)')
molSize=(900,300)
mc = Chem.Mol(mol.ToBinary())
if not mc.GetNumConformers():
    #Compute 2D coordinates
    rdDepictor.Compute2DCoords(mc)
# init the drawer with the size
drawer = rdMolDraw2D.MolDraw2DSVG(molSize[0],molSize[1])
#draw the molcule
drawer.DrawMolecule(mc)
drawer.FinishDrawing()
# get the SVG string
svg = drawer.GetDrawingText()
# fix the svg string and display it
display(SVG(svg.replace('svg:','')))


texts: Why is potassium bitartrate so insoluble?

texts:
The solubility of potassium bitartrate in water at 20°C is given by Wikipedia as 0.57 g per 100 ml, which is considerably lower than that of sodium bitartrate. Generally, a potassium salt is more soluble than the corresponding salt of most other metals—in particular, more soluble than the sodium salt. For example, potassium hydrogen oxalate is more soluble than the corresponding sodium salt (in H₂O at 20°C). Tartaric acid itself is highly soluble.* Is there something special about tartaric acid, or are there other potassium salts of highly soluble organic acids that have markedly low solubility?

*133 g per 100 ml for either optically active acid. (Curiously, and probably irrelevantly, the racemic mixture has much lower—albeit still high—solubility: 21 g per 100 ml.)


texts: Arrhenius equation in exothermic reactions

texts:
According to the Arrhenius equation, the rate of reaction increases when the temperature increases. But according to Le Chatelier's  principle, the reaction rate decreases when the temperature increases.

So is Arrhenius equation applicable on exothermic reactions?


texts: How many monochloro products including stereoisomers of the given compound are possible?

texts:
I tried solving problems and I got 2 products.

However according to my book the answer is 3 products.


texts: Calculation of the lowest energy conformation with a webbased solution or freeware

texts:
I like to draw a molecule in different conformations in a) website or b) freeware and

Calculate its relative energy difference (for example to the lowest global energy conformation)
Display the lowest energy conformation

I'm particularly interested in the calculation of diaxial interactions, gauche interactions, double gauche pentane interactions (and less in ring strain, like chair / half-chair / twisted rings).

I know there are plenty of tools for modelling conformational and electrostacic properties. Most of those are not freely available. Do you an easy solution?
It does not must to be the most precise one, relative energy differences in steps of 0.1 kcal/mol between two drawn conformations would be fine for me.

May be this question is off-topic, because it's a software request, but I didn't know where else I could ask this question.


texts: How to prevent dripping when using a Pasteur pipette with solvents like diethyl ether?

texts:
I'm trying to use a Pasteur pipette for pipetting diethyl ether and regardless of the angle I hold the pipette at, the diethyl ether will automatically start dispensing itself (I am unsure of what this phenomenon is called). I'm sure it's not the rubber bulb since I've been using the same one for pipetting other solvents that don't do this. I've also tried using a different rubber bulb, but to no avail.

Is there any way to prevent this from occurring? If not, is there anyway to mitigate the flow rate of the drips?


texts:
The problem is :

In which of the following compounds does Cl have the most positive partial charge?

SCl2 ,, HCl  ,, BrCl  ,, OCl2 ,,

before I go through how I will solve this problem .. There is a question : Can Cl have a partial positive charge?

Well, all of them are polar, so there is a partial charge on each one of them

but how to compare or specify the partial charges?

The only thing I can think about is electronegativity

is it like .. the greater the difference in electronegativity the more the partial charges ?

Or .. ?


texts: Calculate pressure equilibrium constant from concentration equilibrium constant

texts:
$$\ce{N2(g) + 3H2 (g) -> 2NH3(g)}$$
  Calculate $K_\mathrm p$ from $K_\mathrm c$, given that $K_\mathrm c = \pu{4.2 M^-2}$
  and that there is 0.2 moles of $\ce{N2}$, 0.6 moles of $\ce{H2}$ and 0.425 moles of $\ce{NH3}$. Temperature = $\pu{600K}$

My attempt at the question:

$K_\mathrm p= K_\mathrm c(RT)^{\Delta n}$

$K_\mathrm p= 4.2(8.314\times600)^{-2}$

$K_\mathrm p= \pu{1.69\times10^{-7} Pa^-2}$

However, in our answer sheet the value of $K_\mathrm c$ is divided by $10^6$ and the answer is $\pu{1.69x10^-13 Pa^-2}$. Could someone please explain why $K_\mathrm c$ is divded by $10^6$?


texts:
I am unfortunately not very good at chemistry, so I am having trouble figuring out where to start on this project.  I need to have some way of get some amide functional groups stuck on a substrate (most likely some glass beads or slides) so I can try to show some interactions of the amide with a molecule I am interested in.

Does anyone know of any literature that shows a good way to functionalize silica with amides?

Thanks for any help with this, I really appreciate it.

EDIT: I found some of this stuff ((3-Aminopropyl)triethoxysilane) in our lab.  Could I just put a glass slide in it and leave it over night?
Then maybe come back and wash acetyl chloride over it as in this reaction?


texts: Phosphorus halides react with alcohols to give alkyl halides. I think that a similar reaction would be possible with sulfur halides. In particular, sulfur iodides. While these are not stable at room temperature, they could hypothetically exist as intermediates, and quickly react with the alcohol solvent they are in. Simply combining sulfur and iodine in an alcoholic solution, with stirring and a hot water bath might be able to form this intermediate. Do you believe that such a method would work? I attached a reaction mechanism below.


texts: Electron transfer rates in Marcus Theory

texts:
Electron transfer rates (k) as derived from Marcus theory assumes i) thermal equilibrium and ii) neglects quantum nature of low-frequency phonon modes. Can anyone explain what is at the heart of these two assumptions? Thanks a lot!

I read this in the context of the electron transfer process in organic semiconductors.


texts:
Recently we had this challenge in our Organic Chemistry Department.
I was not involved in it but I thought it might be interesting for the SE Chemistry site, so here it is.

Propose a structure for C20H18 with the longest IUPAC name.
Following rules apply:

Names must be generated with MarvinSketch: Structure>Generate Name…>Preferred IUPAC Name (https://www.chemaxon.com/products/marvin).
No isotopic markings can be used.
The structures must be possible (no cycles with too much unsaturations nor systems with impossible tension).
All the characters will be counted: numbers, letters, points, colons, dashes, everything.
Longest name wins.

Here is the example that was given:

and the name provided by MarvinSketch:

(1'R,4'Z,6'Z,8'Z,10'Z,12'S,15'R,16'R,17'R)-spiro[cyclopropane-1,18'-tetracyclo[13.2.1.04,17.012,16]octadecane]-2,2',4',6',8',10',13'-heptaene

141 characters

Good luck and prosperous year 2018!

EDIT

Well, what is a challenge without a prize?
So, I have set a bounty worth +50 reputation for the longest name.
Sorry, I can not spend much more on it.
Remember that you can post more than one structure.
If you have proposed one and after some days you find a structure with a longer name, you can post it too.


texts: I've been teaching chemistry for 25 years, but now I'm confused.  Is a colloidal dispersion a heterogeneous or homogeneous mixture? I've seen both answers on the web.


texts: Why is the atomic mass unit less than the mass of both a neutron and a proton?

texts:
The atomic mass unit is $1.6605 \times 10^{-27}$ kg.
This is less than the mean of the masses of 6 protons and 6 neutrons.
How do we account for the lower mass ?
My understanding is that some of the mass is in the form of energy somewhere, in the bonding maybe or in the kinetic energy.
Can someone clarify where this mass is please ?


texts: Why does acetic acid combined with dirt turn blue?

texts:
Around my faucet was some mysterious dirt from a previous tenant. I poured acetic acid with a concentration of 25 percent over it. I came back after a few hours and noticed some blue stains which hadn't been there before. What is this blue substance? Is it poisonous? What must have been in the dirt to produce this?

In Wikipedia I came across a statement about acetic acids and blue color:

  A more sensitive test uses lanthanum nitrate with iodine and ammonia to give a blue solution.

Could the mechanism described there be what I'm looking at? Is it really possible that this dirt contains lanthanum nitrate?


texts: Are the names for chemical elements the same in both modern Greek and classical Greek?

texts:
I am curious whether the modern Greek names for chemical elements were adopted from Classical Greek, both Latin and Classical Greek, or some international standard?
I'm unsure if this is the correct place to address this question as there's no Greek SE site and meta seems a bit open ended about it.


texts: Why do we need sulfuric acid in creating alkyl bromide and not in creating alkyl iodide from alcohol and hydrogen halide?

texts:
i) $\ce{R-CH_2-OH + HBr   ->[H_2SO_4] R-CH_2-Br + H_2O}$

ii) $\ce{R-CH_2-OH + HI   -> R-CH_2-I + H_2O}$

What role does sulfuric acid play in the first reaction?
Why are we not using it in the second one?


texts: Explanation of metallic crystal structures using orbitals and electron configuration

texts:
There has to be a direct relation between metallic crystal structure formation and electrons in orbitals. For instance, we know that Fe2+ forms body centered cubic or bcc structure with the coordination number of 8, which means each Fe atom bonds with 8 others after getting rid of the two electrons in the 4S orbital.

The electron configuration of one Fe2+ would look as follows:

1s2  2s22p6  3s23p63d6

The problem is, that I do not see how Fe2+ would react with 8 others, based on the electron configuration and the octet rule, to form bcc structure.


texts: Is this approach to finding density in crystal lattice acceptable?

texts:
In answering a question in an elementary chemistry text that asks for the density of gold ($\ce{Au}$) based on crystal dimensions and weight per atom, I found the approach I used was a little different from that of the book and wanted to see if this is reasonable.

Gold crystal cells are face-centered cubes of a given length edge and a given weight per atom. The book reasons that since each of the 8 corner atoms is shared by 8 cells and each of six face atoms is shared by 2 cells, each cell adds $8/8+6/2 = 4$ atoms to a crystal structure - which gives the correct density.

My approach was to count all the atoms in a cube of cells and disregard sharing, since as long as the count was accurate the average number of atoms per cell would be correct in the limit.

For example: in a cube of 8 cells, there are $3^3$ corner atoms and $3\cdot 2^2(2+1)$ face atoms. So the general formula is $(n+1)^3+3n^2(n+1)$ atoms in an $n \times n$ cube. But in $n^3$ cells the ratio $r$ of atoms per cell to cells is

$$r=\lim_{n\to\infty} \frac{(n+1)^3+3n^2(n+1)}{n^3}=4$$

  So this also gives the correct density, and my question is whether there is anything wrong with this approach?

(In an earlier version of this question I failed to count all the face atoms; hopefully this is easier to follow.)

[Edited to correct formula.]


texts: The time-dependent pH value in a fermentation

texts:
I want to know if someone has supporting tips or solutions to my problem:
In biotechnology, fermentations are used to grow microorganisms. These need a specific media/broth in which temperature, pH, substrate and many other factors conclude to an optimum. Only if the surrounding broth is in optimal condition for the individual microorganism, the microorganism will grow as best as possible.

In my media the broth is buffered with $[\ce{HA}] = \ce{H2PO4^-}$ and $[\ce{A-}] = \ce{HPO4^2-}$.

While the fermentation is running the pH is corrected by $2\ M\ \ce{NaOH}$ which is pumped into the broth. Via balances, the weight is recorded and the input can be calculated.

I know the initial concentrations of my buffer solutions and the concentration of the base that is dropped into at every minute of record.

How can I calcute the pH for an individual timepoint in my aqueous fermentation? My tries via the Henderson-Hasselbach-formula did not work so far...
(Neglecting other surroundings such as stirring, the other media components, the biomass' metabolites, temperature influence on the pKs, etc.),

Thanks in advance!


texts: Practical considerations for electrolysis of water

texts:
I'm interested in electrolysis of water to form O$_2$ and H$_2$, as pure as possible given the constraints of a "household chemical" setup. I've read other questions on here (in particular, Best Settings for Electrolysis of water, Does the electrolysis of water produce chlorine gas?, Why would water, and not saltwater, undergo electrolysis? and others), but still have some open questions, in particular concerning the used electrolyte and the material of which the anode/cathode are.

Electrolyte

I'll be using tap water for my reaction that is not chlorinated. However, unspecified salts/impurities might be present that I cannot closer define, but we're talking about infant-safe drinking water (with little Na present). To have an efficient reaction, I will need to dissolve an electrolyte. There are many choices:

NaOH (lye): As far as I can tell, the "ideal" candidate for my requirements, but might not be present in a household and might be difficult to obtain. Should form pure H$_2$ and O$_2$ if I am not mistaken.
NaCl (table salt): Present in every household. Greatest drawback is that as far as I read Chlorine gas is formed during the electrolysis. My question would be, is the Chlorine emitted at the H$_2$ or O$_2$ electrode?
NaHCO$_3$ or KHCO$_3$ (baking powder): Present in every household. Does not form Chlorine gas. However, as far as I have read, forms CO$_2$, but again I'm unsure at which electrode.

Electrode material

We can forget platinum and gold right off the bat for price reasons. Stainless steel would be a good choice, but I've also read that pure Nickel sheets should be working well. My main concern is corrosion and passivation of the electrode material which then slows down the overall reaction. Would Nickel sheets be preferrable over stainless steel? If we use some material that does corrode easily (e.g., regular steel or just run-of-the-mill hardware store items that are some combination of galvanized iron), would the corrosion and solutoin of the metal in the water affect the gas quality? If so, how?


texts: How to draw molecular orbital diagrams for protonated/deprotonated methyl red?

texts:
Give a molecular structure-based explanation for the differences in the UV-Vis
spectra in I and II. Use detailed MO schemes for A and B for illustration. (12 marks)

Does the double bond of N=N, C=O and lone pair of oxygen and nitrogen involved in the MO diagram?


texts: Is there a well defined way to discern the hybridization of a nitrogen atom in ring, like pyrrole? How can you know whether the nitrogen's lone pair are in the conjugated system or not?


texts: What happens to the hydroxide anion during the electroreduction of water?

texts:
The reduction of water at a cathode is represented by the following equation:

Cathode (reduction): $\ce{2 H2O_{(l)} + 2e^{−} → H2_{(g)} + 2 OH^{-}_{(aq)}}$

If this is done in a divided cell, what would happen to the $\ce{OH-}$ anions? The hydrogen gas would accumulate and bubble would form. Would the $\ce{OH-}$ anions just build up in the solution? Do they interact with each other naturally forming $\ce{H2}$ and $\ce{O2}$?


texts: Can you create a temporary bond in between an atom and a filter by electrically charging the filter?

texts: I want to be able to turn a filter on and off by electrically charging the filter so that it creates a temporary bond that blocks up the filter then, by discharging the filter, releasing the temporary bonds and allowing particles through again. Is this possible?


texts: What are compounds with the same mass called?

texts:
It may be that the answer is just "no" and that's why I can't find it, but is there any common name for compounds with the same mass?

I'm thinking in the context of mass spectrometry where these compounds require additional steps to resolve.

Isomers are the obvious example, but I was wondering if there was a more general term.


texts: Why is there a need of polar coordinates to solve the Schrödinger wave equation for the hydrogen atom?

texts:
Why is there a need of polar coordinate to solve the Schrödinger wave equation for the hydrogen atom?
I went through some standard text books but I am feeling rather confused about the explanation.


texts: Clarification in the mechanism for Molisch's test for glucose

texts:
Wikipedia says

  Molisch's test is a sensitive chemical test, named after Austrian botanist Hans Molisch, for the presence of carbohydrates, based on the dehydration of the carbohydrate by sulfuric acid or hydrochloric acid to produce an aldehyde, which condenses with two molecules of a phenol (usually α-naphthol, though other phenols such as resorcinol and thymol) also give colored products), resulting in a red- or purple-coloured compound.

Can somebody provide an arrow pushing diagram to illustrate the intermediate steps of these reactions? (especially for the dehydration of glucose)
Also, for the reaction with of 5-(hydroxymethyl)furfural with 2 moles of phenol, it seems that the acyl group is acting like an electrophile and naphthol is engaged in an electrophilic aromatic substitution, but then again, I am not sure how 2 moles of naphthol combined there. Any help would be appreciated.


texts: Why does eutectic point have three phases, but consolute point have only two phases?

texts:
At eutectic point, there are three phases: solid A, solid B and homogenous liquid phase containing both A and B.

But at consolute point, we are told it has 2 phases: liquid A and liquid B.

Why isn't there a homogenous phase containing both liquid A and B at consolute point just like an eutectic point?


texts: Bromination on the aromatic ring vs aliphatic chain

texts:
I thought that the answer would be a simple electrophillic aromatic substitution and as the carbonyl is a meta director, the bromine would be present meta to the group.

But the given answer was the α-brominated compound and is also found out an article which says that this happens in case a catalytic amount of $\ce{AlCl3}$ is used while the bromine is substituted in the ring if a larger amount is used. How does this happen?  Why does the amount of $\ce{AlCl3}$ matter?


texts: On stretching a rubberband does the entropy increase or decrease?

texts:
It seems that on stretching a rubberband, entropy or the degree of disorder is likely to increase. Is this the correct answer?
My text says that on stretching, the arrangement of particles become more 'ordered' and hence entropy 'decreases'. How?


texts: My textbook says that in a galvanic cell, it's not possible to measure single electrode potential independently. Instead, a Standard Hydrogen Electrode is used as the system is under equilibrium. Can someone explain this concept more clearly?


texts: Stronger ESI signal for deuterated substances

texts:
I observe a constant phenomenon in my ESI measurements, which indicates that deuterated substances give a stronger signal than the same substance in non-deuterated form. Unfortunately I can't make any sense of it, because I can't see any reason why a deuterated substance should be protonated any better. Since I have not seen or read anything about this phenomenon so far, I would be very pleased if someone could clarify whether this is something well known, or whether my samples just happen to show the same artifact over and over again. If it is a known phenomenon, I would also be happy to hear an explanation.
Further bits of information: LC-MS/MS in ESI mode, same acquisition method for both forms of the compound, observed in EPI scans, increase in intensity c.a. 3-fold.
To make this very clear, the two compounds (deuterated and non-deuterated) are measured separately in separate vials with a blank in between, so no co-elution can occur. One measurement is done with a solution of 100 ng/mL estradiol in acetonitrile and one with 100 ng/mL estradiol-d5 in acetonitrile. They are not mixed!


texts:
Phase diagrams tell how a given substance changes it’s phase with pressure and temperature. While most sources discuss this in detail, none of these mention whether or not evaporation is taken into account when drawing the diagrams .
Any liquid can evaporate regardless of the temperature, given that the molecules have the needed kinetic energy. So, do phase diagrams take this into account?


texts: How can either reactants or products be "favored" at equilibrium?

texts:
From Atkins' Elements of Physical Chemistry (6th ed.):

  $$\Delta G_\text{r}^\circ = -RT \ln K \tag{8}$$
  This fundamentally important equation links thermodynamic quantities – which are widely available from tables of thermodynamic data – and the composition of a system at equilibrium. Note that:

  If $\Delta G_\text{r}^\circ$ is negative, then $\ln K$ must be positive and therefore $K > 1$; products are favored at equilibrium.
  If $\Delta G_\text{r}^\circ$ is positive, then $\ln K$ must be negative and therefore $K < 1$; reactants are favored at equilibrium.

It says products/reactants will be favored at equilibrium, but I thought at equilibrium neither are favored?


texts: Transition metal order of filling electron

texts:
There is a specific order for filling electron for transition metals, but I don't know if it applies to other elements too?

Some thing to take note of in this picture is the order of 3d and 4s. My belief is: 3d has a higher energy level than 4s, and but 4s is still the outermost shell.

The reason that transition metal would form colorful ions is that there are empty or half filled d orbitals, so when excited electrons drop back to the d orbitals, they emit energy in form of light. I am a bit confused about this.( it is from a book) what electron is it referring to? Is it the d electron or electron of lower energy level orbitals, as for instance 3p?


texts: Looking for advice regarding a larger scale soxhlet extraction

texts:
I have successfully completed a few soxhlet extractions at a much smaller scale using a soxhlet extractor with ~200ml capacity.  With that, I was able to extract from ~100g of pre-powdered, sonicated leaf with good results.

I'd like to extract a total of 1Kg, so I need to scale up. However, this is something I haven't done before. I'm currently looking into soxhlet extractors with a much higher capacity.  I found a Soxhlet extractor on eBay with a capacity of 1000ml with 34/45 lower and 71/60 upper joints.  I have also found a 16" 4-bulb Allihn condenser (71/60).

I plan first to defat the leaf with hexane, then extract with methanol since the alkaloids I'm after (Mitragynine) are highly polar.

Questions:

This condenser seems to have adequate cooling capacity, but I'd feel a lot better if someone could confirm or suggest a better option if there is one.
I'm also curious about what the optimal size flat bottom flask/amount of solvent would be.  After looking at similar apparatus, I'm guessing a 2000ml flat bottom flask with 1000ml of solvent.
Going from a 200ml to 1000ml capacity extractor, am I right to assume I can extract 5x as much powdered leaf?  In this case, ~500g?
This apparatus will be quite heavy, and the center of gravity not ideal.  How best to support it safely?

Thanks in advance!


texts: How to determine the source of PVA: crude or plant-based?

texts:
We're a small startup company looking to make products using ingredients solely derived from plants. One of the main ingredients in one of our products is polyvinyl alcohol (PVA). We have found a company that claims that their PVA is made exclusively from plants, and that no natural gas or crude oil is used in its production.

To provide some extra clarification based on the discussion below this question: PVA is a synthetic polymer prepared by hydrolysis of polyvinyl acetate. Polyvinyl acetate is made from acetic acid and ethylene. Ethylene is often made from natural gas or petroleum. Is it possible to determine whether the original ethylene used to make our PVA is derived from petroleum or plants? If so, can this be done given just the PVA itself, and no other information?

The reason I'm asking is because I want to independently verify the manufacturer's claim that their product is indeed completely derived from plant sources.


texts: Reason behind more Reactivity of Unsaturated Hydrocarbons

texts:
My textbook says that unsaturated hydrocarbons are more reactive than saturated ones. But double and triple bonds are stronger than single bonds.
What is the explanation for this?


texts:
What makes something glow in the dark? The only explanation that I can come up with for what makes things glow in the dark is that there is probably a chemical reaction slowly releasing the light that was previously absorbed. Am I correct?

How does this phenomenon work?


texts:
Which is the stronger acid in the given pairs?

  $\ce{HClO3}$ and $\ce{HBrO3}$
  $\ce{HClO2}$ and $\ce{HClO}$
  $\ce{H2Se}$ and $\ce{H2S}$

given that the number of oxygen atoms is the same, the most electronegative atom should result in a stronger acid, thus $\ce{HClO3}$ is stronger.
$\ce{HClO2}$ is stronger since it has more oxygen atoms.
Here's where my logic fails, since the structure is the same (both have $\ce{2H+}$) then it boils down to 2 things to account for: electronegativity and the size of the atom. Going with electronegativity, sulfur is more electronegative thus stronger acid  which was my original answer. But, the correct answer is $\ce{H2Se}$ is the stronger acid which implies in this case atomic size ($\ce{Se}$ is larger than $\ce{S}$) outweighs electronegativity. I do not understand why in this case $\ce{H2Se}$ is stronger than $\ce{H2S}$ given sulfur is more electronegative, and most importantly why the same logic used in 1. can't be applied here and how do I discern where to account for atomic size specifically or when to account for electronegativity?

Any detailed-dumbed down explanations  on the logic are highly appreciated.


texts: Is it possible to remove salt from food without changing the flavor?

texts:
I love soup, even a thick soup for dinner, yet many soup products have 400 to 1000 mg of sodium in them. Is there a simple chemical procedure any consumer could do to take the sodium out of the product without 'hurting' the flavor?

If one takes some, say, Campbell's soup and heats it to boiling, then freezes it, then heats it again, then freezes it etc., would this extract some sodium?


texts: How does the force constant change when a heavier atom is used in vibrational spectroscopy?

texts:
(iii) The fundamental band in the IR spectrum of $\ce{^1H^{127}I}$ is found at $\pu{2308 cm^-1}.$ Calculate the force constant for the bond. Assume the molecule can be treated as a harmonic oscillator.
(iv) Calculate how the position of the fundamental band would be expected to differ for molecules of $\ce{^2H^{127}I}.$

I have found the force constant in (iii), but I am struggling with (iv). I don’t know how to calculate the difference. Any insight would be greatly appreciated.


texts:
This was a question on a review sheet for Lewis structures.

Now I could draw $\ce{SO4^2-}$ with no issues, but I can't make sense out of $\ce{SO4^2+}$ because I can't even make bonds to all $\ce{O}$ without exceeding the number of bonding electrons.

This is on a high school AP review so it is possible that there are exceptions to the normal rules, but I can't see how any of them apply. I could just chop electrons off the oxygens and leave it depleted, but I don't imagine that is a stable form of a cation which would exist?

A quick check doesn't turn up anything so is this a real thing or was it just a typo?


texts: Mechanism for simultaneous reduction of nitro group (into aniline) and aromatic substitution (into benzonitrile) by Ethyl cyanoacetate?

texts:
I stumbled upon this paper when I'm trying to look at established protocol to synthesize one of the compounds (compound IIk) mentioned in the paper.
Studies on Aromatic Nitro Compounds. V. A Simple One-Pot Preparation of o-Aminoaroylnitriles from Some Aromatic Nitro Compounds

The paper described transformation of aromatic nitro compounds into o-aminoaroylnitriles by ethyl cyanoacetate in the presence of strong base. While the general scheme showed fused aromatics, this reaction also works for any electron-withdrawing (in addition to the nitro) containing single aromatics.
I have replicate the reaction for compound IIk and I was abled to purified the compound with yield consistent with what was described in the paper.
I have never seen this kind of transformation before, especially with ethyl cyanoacetate. The paper itself mentioned that the mechanism is unknown and I haven't found any subsequent papers that try to elucidate the mechanism.
Anyone has any idea how this reaction works?


texts: Rate of substitution and elimination reactions at high temperatures

texts:
From High School, I've been reading that elimination reactions are favorable at high temperatures because their entropy change is positive, so at higher temperature the Gibbs free energy will be more negative so the equilibrium will be more towards product's side.

But I've encountered a different statement in Clayden's Organic Chemistry:

  This explanation is simplified because what matters is the rate of the reaction, not the stability of the products. A detailed discussion is beyond the scope of the book, but the general argument still holds.

So what is the reason behind this? Why are substitution reactions not that much faster at high temperature than elimination reactions?


texts: Why do we call a benzene ring attached to an hydroxyl functionality an alcohol and not a benzene?

texts:
But if an alkyl group is attached to a benzene ring, we call the parent chain the benzene ring, no matter how many carbons the alkyl group has. Why? For example: heptylbenzene.

For another example: when 1-propenyl-benzene reacts with sulfuric acid we get 1-phenyl-1-propanol. We don't call this product 1-propanol-1-benzene.


texts:
I have seen questions regarding EA but they were all about the 1st EA so this question is not duplicate.

I came across a statement which goes like "2nd EA of halogens is almost zero". How is this possible? How can energy gained/released on adding an electron be almost 0, particularly when we are adding an electron to a noble gas, because, according to me, a lot of energy is required to do this.


texts: I would like to know if there are any gels that would increase in volume or swell due to electric field or current?!


texts: Looking at the structure of an amino acid (as a zwitterion), it seems that the part of the molecule with the amino group and the carboxylic acid group are quite polar (the amino group has a positive hydrogen and the carboxylic acid group has a negative oxygen). However, my textbook says that the character of the R group completely determines the polarity of the molecule (i.e. if R is non-polar, the molecule is non-polar). Why is this?


texts: How to display ligands as ball and stick and macromolecules as cartoons (if protein) / rings (if nucleic acids) in Avogadro?

texts: Avogadro has many good qualities but I can't seem to find a way to display ligands differently to macromolecules in the same view window. Frankly I can't seem to find a way to display any two things differently (like one as ball and stick, another as ribbons, or w/e) to one another in the same view. It seems like in a given view window everything has to be displayed the same way, there's no room for making one part displayed one way and another part displayed another way.


texts: When pH increases, does the effect of increased [OH-] or reduced [H+] control precipitation of CaC2O4

texts:
The image below shows how oxalic acid dissociates and forms calcium oxalate ($\ce{CaC2O4}$ or $\ce{Ca(OOC-COO) as written below}$).

When the pH increases, does this result in more or less $\ce{Ca(OOC-COO)}$ forming?

I can think of two factors:

As $\ce{pH}$ increases, $\ce{OH-}$ increases. Greater $\ce{OH-}$ means more of the $\ce{Ca^{2+}}$ will react with $\ce{OH-}$, forming $\ce{Ca(OH)2}$. So the reaction in the third line below will shift to the left, resuling in less $\ce{Ca(OOC-COO)}$.
As $\ce{pH}$ increases, $\ce{H+}$ decreases. Less $\ce{H+}$ results in the reactions (in line 1 and 2) shifting to the right. Hence, there will be more $\ce{(-OOC-COO-)}$ and so more $\ce{Ca(OOC-COO)}$.

These give opposing results. Which one outweighs the other, and why?

The original question from by textbook:

Drinking strong antacids to relieve indigestion produces kidney fluid that is more alkaline than usual.

Are kidney stones more likely to occur under these conditions?

Yes, as at a higher pH a higher concentration of oxalate ions will form.
Yes, as both calcium and oxalate ions are bivalent.
No, as the presence of hydrogen oxalate ion (HOOCCOO–) means that a buffer is present.
No, as the higher concentration of hydroxide ion (OH–) will remove calcium ion by forming calcium
hydroxide.


texts: Is there any special rules for checking the aromaticity of polycyclic compounds?

texts: This question arose in my mind because it's given in a book that pyrene is aromatic. How can it be with 16 π electrons? So, it should be actually anti-aromatic or is there any special rule for these types of compounds?


texts: is ph at eq point dependent on acid concentration at all

texts: Know for a weak acid strong base titration that the ph will be above 7, but does the concentration of the acid affect the ph at the eq point at all?


texts:
I often read that reactive organometallics must be handled under an inert atmosphere because they react with oxygen in the atmosphere. This applies to grignard reagents, organolithium reagents, and organozinc reagents.

What is the reaction of these organometallics with oxygen? I don't see how oxygen can be electrophilic. Maybe it forms a peroxyacid?


texts: Does temperature change pressure in isochoric system?

texts:
Consider the following equilibrium reaction:

$$\ce{2 NOCl (g) <=> 2 NO (g) + Cl2 (g)} \qquad  \Delta H > 0$$

My textbook has a statement that:

  If you decrease the temperature when keeping volume constant, then reaction shifts to the reactants.

I know that since the enthalpy change $\Delta H$ is positive, we can think of the reaction as:

$$\ce{2 NOCl (g) + \text{heat} <=> 2 NO (g) + Cl2 (g)}$$

And according to Le Chatelier's principle we can say that if we decrease the temperature, then reaction favor the side have heat in it. This comes me so reasonable but there is one more thing we have to consider in my opinion: pressure.

While keeping volume constant, decreasing temperature will decrease also pressure. So reaction will favor the side that have more molecules in it. In this case, it is the opposite side of the previous one.

Is my reasoning true? If it is, how can I conclude the side determining job?


texts: Why tautomers are considered to be the same chemical compound?

texts:
Because of the rapid interconversion, tautomers are generally
  considered to be the same chemical compound. (Wikipedia)

But looking at the examples provided on that same Wikipedia article, it is obvious that different chemical reactions would take place in each case (for example enol vs. keto).

(source)


texts:
I notice that salt solutions of $\ce{NaCl}$ and $\ce{KCl}$ are colourless while those of $\ce{CuSO4}$ and $\ce{FeSO4}$ are coloured.

I got as far as figuring that it has to do with the transition metal ions, but I can't explain why the salt solution of $\ce{ZnSO4}$ is colourless even though zinc itself is one of the transition metals.


texts: Lower Heating value calculation from chemcial combustion equation of Butane

texts:
QUESTION
    Butene, C4H8 is burned in an engine with a fuel-rich air-fuel ratio. Dry  analysis of the exhaust gives the following volume percents:                   $\ce{CO2} = 14.95%$, $\ce{O2} = 0%$, $\ce{CO} = 0%$, $\ce{H2} = 0%$, $\ce{C4H8} = 0.75%$, with the rest being $\ce{N2}$. Higher heating value of this fuel is 46.9 MJ/kg. Write the balanced chemical equation for one mole of this fuel at these conditions. Calculate the air-fuel ratio, equivalence ratio, lower heating value of the fuel, and energy released when one kg of this fuel is burned in the engine with a combustion efficiency of 98%.

My attempt at solution:
I write the stoichiometric equation like so:
$$ \ce{C4H8 + \frac{1}{\phi}(4+(8/4))(O2 +3.773N_2)\rightarrow n_1 C4H8 +n_2 CO2 +n_3 H2O}$$
where, $\phi$ is the equivalence ratio(a engineering term used to describe the ratio of $(F/A)_{\text{actual}}$ to $(F/A)_{\text{stoichiometric}}$.

So,now I have 3 unknowns, $n_1$, $n_2$ and $\phi$.

I unfortunately get $n_2=0$ after doing the mole balance of carbons,hydrogen and nitrogen.

I understand that the percentages given by volume are the mass fractions which should later form a separate equation. But, I still get $n_2=0$. Where have I gone wrong?(Should I still consider putting in $\ce{O2}$ and $\ce{CO}$ into the above equation even though their %by volume are zero?)


texts: The above is a picture of Galvanic cell. Zinc anode is placed in Zinc sulfate solution so we have ions as Zn2+ and SO42-. On the cathode side we have the same situation we have Cu2+ and SO42-. My question is why the zinc rod is getting converted into zinc ions and copper ions are getting converted into atoms and get deposited on copper rod. Why is electron flowing from anode to cathode?


texts:
I was doing some problems from the textbook on converting between units using dimensional analysis and I came across this problem.

A vat of Hydrogen Peroxide ($\ce{H2O2}$) contains
455 grams of oxygen atoms. How many
molecules of ($\ce{H2O2}$) are in the vat?

Sorry if I didn`t format the question correctly, I am a still a newbie.
But how would I set this up? I would not like the answer to this question but I would like some input on how would I get how many molecules of hydrogen peroxide from grams of oxygen atoms? Any help would be much appreciated. Thanks in advance!


texts: What happens to water under high pressures without possibility of escape?

texts:
Knowing very little about the nature of water, wondering how it might behave at the centre of a planet or centre of an another massive gravitational body.

Could water take such pressures or might it break into separate hydrogen and oxygen to find something more accommodating for the pressure exerted, if such atmosphere would allow the volume even?

Finally, bonus points: could triple points in water play a role in keeping temperatures low under high pressures via fluid thermodynamics?


texts: Rate of hydrolysis of ester in presence of an acidic medium

texts:
Does the rate of hydrolysis of an ester depend on the concentration of both the ester and the acid, or only the ester?

I was told by my professor that hydrolysis of ester follows a pseudo-first order reaction: as the amount of water present for the reaction is very large, the change in concentration of acid/base will result in very negligible changes in concentration of $\ce{H+}$/$\ce{OH-}$ ion. So, the rate is only proportional to the concentration of ester taken.

Can someone explain if the above is in presence of basic medium or acidic medium?


texts: What do the prefixes meta, ortho, pyro mean in inorganic chemistry?

texts:
In inorganic chemistry, when is the prefix meta used? (as in metaborate and metasulphite)
What about the terms pyro and ortho (as in orthophosphorous acid)?

For example, I recently came to know about the prefixes per and hypo which are used to refer to the highest and lowest oxidation states of an element respectively (like perchlorate and hypochlorite).

Are there any terms and conventions I should be aware of?


texts: Will bleach combined with any of these chemicals create poisonous gas?

texts:
I need to know if a combination of bleach and the chemicals below will create poisonous gas. Will it create chloramine, and will there be any visible gas?

1) Sodium laureth sulfate
2) Sodium citrate
3) C12-14 Pareth-3


texts: What are the steps to integrate the common rate law to find the integrated rate law for any order

texts:
I cannot find any sources that actually list the steps for integrating a rate law, and it’s been driving me crazy. My Ap chem 2 teacher doesn’t know how to do it and just wants me to memorize the common rate laws, however I don’t memorize equations unless I know how to write them out and where they come from. I have the equation

$$ \text{rate} = \dfrac{\mathrm d[A]}{\mathrm dt} = k \cdot [A_0]^{n} $$

where $n$ is the order of the equation
$[A_0]$ is the concentration at time $0$
$[A]$ is the concentration with respect to time
$k$ is the rate constant

I know that for a first order ($n=1$) reaction the equation becomes

$$ [A] = [A_0] \cdot \mathrm e^{kt} $$

and that a second order ($n=2$) reaction the equation is

$$ [A] = \dfrac{[A_0]}{1 + kt \cdot [A_0]} $$

But I don't know what the steps are to find these equations. If I find that the order of my equation needs to be 1.5 ($n=1.5$), I will have no Idea what the equation will be.

From these equations I will know most of the time $[A_0]$, $[A]$ and sometimes Rate.

Edit:

After following the links I learned a portion of the process to solve the equation for any $n$. However after testing it out I am either getting a incorrect answer of a incomplete answer

$$ [A] =\int_{[A_0]}^{[A]}{\frac{1}{[A_0]^2}\,\mathrm d[A]} = \frac{[A_0]^{1}}{1} = \int_{0}^{t}{k\,\mathrm dt}$$

the answer should be

$$ [A] = \dfrac{[A_0]}{1 + kt \cdot [A_0]} $$

what parts am I missing?


texts: Why are cations ordinarily smaller than anions?

texts:
I'm reading on ionic crystal structures and am confused by this from my textbook:

  Because the metallic elements give up electrons when ionized, cations are ordinarily smaller than anions

I understand that having a positive charge will pull the electrons closer, but shouldn't the atom from the larger period (row on periodic table), have more electron shells and be the larger atom?


texts: What are the conditions for using skeletal replacement ('a') nomenclature?

texts:
The Blue Book 2013 in P-63.2.4.1 gives “1-methoxy-2-(2-methoxyethoxy)ethane” as the IUPAC preferred name for $\ce{CH3OCH2CH2OCH2CH2OCH3}$ and comments,

  Skeletal replacement (‘a’) nomenclature [method (4)] generates preferred IUPAC names, when the conditions for using this type of nomenclature are met (see P-15.4); otherwise substitutive nomenclature must be used.

It then names $\ce{CH3OCH2CH2OCH2CH2OCH2CH2OCH3}$ as “2,5,8,11-tetraoxadodecane.”

My question is why skeletal replacement nomenclature was used in the latter case but not the former—why the conditions for using skeletal replacement nomenclature are not met by the former molecule.

P-15.4 states that

  “Skeletal replacement (‘a’) nomenclature is used in two ways:

  “ (a) …

  “ (b) to generate simpler names for heteroacyclic structures than those formed by following the principles of substitutive nomenclature, for example, in naming polyamines, polyethers, etc., by replacing carbon atoms in corresponding acyclic hydrocarbons” (89).

The former molecule seems like an instance of a polyether, and the name “2,5,8-trioxononane” seems simpler than the given preferred name, so it seems that this molecule meets the this criterion.

What factor led to the use of substitutive nomenclature where replacement nomenclature seemed to apply?


texts: Now I know it's something related to the fact that $\ce{CCl4}$ does not have a net dipole moment but I can't connect the dots.


texts: Confused about the direction in which the bond will break

texts:
Why does the bond break in different fashion in the two cases?

For case X, a 3° carbocation is formed, bit why isn't this the scenario for case Y?

A 3° carbocation is anyday more stable than a 1° carbocation, isn't it?


texts: Why does the transverse magnetization in Fourier Transform NMR consist of Ix+iIy ($\hat{I}_{\!x}+\mathrm{i}\hat{I}_{\!y}$)?

texts:
More specifically, the expression for the average expectation value of the transverse magnetization has the following form:

$$M^+(t)=N\gamma \hbar\,\text{Tr}(\hat{\sigma}(t)\hat{F}^+)$$

with $\hat{\sigma}(t)$ the density matrix. $\hat{F}^+$ is defined as:

$$\hat{F}^+ = \sum ^{K} _{k=1} \hat{I}^+_{\!k} = \sum^{K}_{k=1} (\hat{I}_{\!kx} + \mathrm{i}\hat{I}_{\!ky})$$

I don't really see how you intuitively obtain such an expression for the transverse magnetisation (in the syllabus it was posited, not derived). On the other hand, if you would take the complex modulus then you would find the magnitude of some 2D vector. It still does not motivate (enough) for me why it should look like this. Doesn't measurement happen in a single direction? Why is it not just

$$\sum^{K} _{k=1} \hat{I}_{\!kx}?$$

It also bears resemblance to the raising operator (which would explain the $+$), perhaps you measure how many quanta are absorbed, which corresponds to measuring the amount of spins that you raise to a higher energy level (but that's not what the raising operator signifies I think)? Or is it a phasor with a $90^\circ$ angle between both components?


texts: I have been working with thermochemistry at school for a while. I have been introduced to the two terms: formation enthalpy and bond enthalpy. However, I have not quite understood the difference between the two and would be very glad if someone could explain it!


texts: Yellow-amber debris above water filter: What is it?

texts:
I have some weird, yellow-amberish pebbles that have been filtered by my Zero waterfilter. Any idea what they are? Copper maybe?

The black stuff is charcoal from the filter.

The quality of the water in my area is fairly good, with a TDS of 40-60. With the filter, I have a TDS of 0, which is excellent. But I'm still curious as to what those things are.


texts: Definition of major, minor, and trace elements in analytical chemistry

texts:
What is the definition of major, minor, and trace elements in a sample? I am unable to find this anywhere on the internet. Is it something like:

Major elements are those > 0.1 %

Minor elements are those > 100 ppm < 0.1 %

Trace elements are those < 100 ppm


texts: Impact of detergent on internal living tissue?

texts:
There was some spirited debate between the members of my chemistry lab today about the theoretical consequences of ingesting a large amount of the detergent Triton X-100 at a 100% concentration. The MSDS provided by Sigma Aldrich indicates that it is "harmful if swallowed," with a LD50 of 1800mg/kg in rats, but does not provide further detail.

Given that it is capable of decellularizing animal-derived tissues, would it literally "wash" one's extracellular matrix of its cells after degrading the lipid bilayers?

If Triton X-100 is incapable of doing so, are there more powerful detergents that would pose a genuine threat if ingested?


texts: Difference required for compound to be a phenol vs benzene compound

texts:
When naming organic compounds, how should one decide whether a compound should be named as a benzene compound, or as a phenol?

For example, the compound 3,4-dihydroxybenzoic acid has an -OH group, so why is it not named as a phenol derivative? I feel like I'm missing something here, but none of the numerous sources I've looked at have provided a clear-cut rule to differentiate with.


texts: Disparity between LeChatelier's Principle and Solutions

texts:
Let's say that there is a solution
$\ce{Na+(aq) + Cl-(aq) <=> NaCl(s)}$
If the above solution is at equilibrium we can say that it is saturated and hence no more Sodium Chloride will dissolve. However, according to LeChatelier's Principle, if we add more Sodium Chloride it will just dissolve. Is there another rule that governs how this kind of dissolution behaves?


texts: Why does the first lithium stationary state have n = 9/4?

texts:
The ionization energy of $\ce{He+}$ is $19.6 \times 10^{-18}~\mathrm{J~atom^{-1}}$. What is the energy of the first stationary state ($n=1$) of $\ce{Li^{2+}}$?

Since the question specifically states that $n=1$, I used the formula

\begin{align}
E &= -2.178 \times 10^{-18} \cdot \frac{Z^2}{n^2}.\\
E &= -2.178 \times 10^{-18} \cdot \frac{3^2}{1}\\
E &= -1.96 \times 10^{-17}~\mathrm{J}
\end{align}

But the correct answer is supposed to be $-4.14 \times 10^{-17}~\mathrm{J}$ and many people are telling me to use $n=\frac{9}{4}$ which gives the right answer but I don't know why I am supposed to set $n$ at $\frac{9}{4}$.


texts: Oxygen Preventing the Formation of Large Organic Compounds?

texts: My textbook tells me that when carbon bonds with oxygen, the electrons are too close to the oxygen, and therefore they cannot just string together and form large molecules like glucose. It goes on to say that because, during photosynthesis, carbon becomes bonded to less electronegative atoms like hydrogen, it becomes more capable of forming larger compounds. Why is that?


texts: Alkyl halides that do not undergo Wurtz reaction

texts:
I am aware that there are many limitations to the Wurtz reaction, notably the inability of 3° Halides to undergo SN² substitution. Instead, they undergo elimination.
I came across a compound, 4-Bromocyclohexanol which apparently doesn't undergo Wurtz reaction. Being a novice at reaction mechanisms (more specifically organic chemistry as a whole), I am unable to figure out the reason behind this. Also, if this is the case, what type of reaction does 4-Bromocyclohexanol undergo with Na in Dry Ether medium?
As a side interest, are there any other notable exceptions with regards to 1°/2° alkyl halides that do not undergo Wurtz reaction?


texts: Is order of reaction defined for nuclear reactions?

texts:
I am asking this question after asking a similar one for spontaneous nuclear decay phy.stack. Link

Order of reaction is defined for chemical reaction. But wikipedia says about spontaneous nuclear decay:

  Another class of first-order reactions is radioactive decay processes which are all first order. These are, however, nuclear reactions rather than chemical reactions.

Spontaneous nuclear decay is governed by nuclear forces for which it follows an exponential form. There can be deviations from the exponential law at very short time and at very time. But, that's under nuclear physics.

But, has anyone tried to extend the concept of order of reaction to other nuclear reactions eg. transmutation, spallation,fission,fusion etc.

Ben Crowell's comment on my previous phy.stack post:

  If you want to make an analogy with chemical reactions, then you should probably be considering nuclear reactions, rather than spontaneous nuclear decay. For example, you could consider the cross-section for neutron or proton transfer reactions as a function of the number of nucleons (mass number) in the target and projectile.

Wikipedia page on nuclear reaction says on rate of nuclear reaction:

  If the reaction equation is balanced, that does not mean that the reaction really occurs. The rate at which reactions occur depends on the particle energy, the particle flux and the reaction cross section.

Question:
Has anyone tried to define order of reactions for nuclear reaction? Even though concept of order of reactions might not be that useful for nuclear reactions, has anyone modified it to work with nuclear-chemistry?

P.S. I am not sure if this question is suitable here. If it isn't, then just migrate it phy.stack.


texts: How to determine the worst resonance structures out of a given set?

texts:
So I was "happily" doing organic chemistry homework when I came across this question:

For 1-methoxy-1,3-butadiene, which of the following resonating structure is the least stable?
$$\begin{align}(\mathbf{a})\ &\ \ce{H2\overset{+}{C}-\overset{+}{C}H-CH=CH-O-CH3} & (\mathbf{b})\ &\ \ce{H2\overset{+}{C}-CH=CH-CH=\overset{+}{O}-CH3} \\
(\mathbf{c})\ &\ \ce{H2\overset{+}{C}-\overset{-}{C}H-\overset{+}{C}H-\overset{+}{C}H-O-CH3} & (\mathbf{d})\ &\ \ce{H2C=CH-\overset{+}{C}H-CH=\overset{+}{O}-CH3}\end{align}$$

I decided to take a look through my textbook to see what I was missing. The rules to compare resonance structure energies (and therefore determine relative contributions) were in my textbook.  It said:

The following structures are considered to contribute most:

Structures having filled octet a for second row elements (C, N, O, F) are stable.
Structures having minimum number of formal charges and maximum number of bonds.
Structure in which negative charge appears on the most electronegative atom (C < N < O).
Structure in which there is minimal charge separation while keeping the formal charges closer together.

Instead of answering my initial question, two more questions came to mind. They are (in order):

Why do the octets of only the second row elements have to be filled in for greater relative contribution?
I suppose it has something to do with the greater electronegativity values of the elements, but would still like some clarification.
From option (a) and (c) in my question, how did the two positive charges get next to each other?

Resonance structures, as stated in my textbook, can be represented by two or more Lewis structures that differ only in the positions of the electrons.
The options clearly do not just redistribute the electrons. Or at least I don't think so.
So if I had to guess, the answer would be (b) because the terminal carbocation is worse than an internal carbocation.
But it turns out, the correct answer is (c). And I think that it shouldn't even be considered a resonating structure.


texts: Is vegetable shortening a fully hydrogenated product or is it partially hydrogenated?

texts: Have the oils used to make vegetable shortening been fully hydrogenated or have they been only partially hydrogenated?


texts: Minimum image convention and the atom “seeing” itself

texts:
The minimum image convention in molecular dynamics can be stated as:

  A particle in the central square must not interact with one of its neighbors in the central square and an image of this neighbor in one of the replicas at the same time but only with the closer one.

What is the basis for this convention? In other words, what is the problem with a central atom seeing another atom from both the image and the central box?

If I look at the simulation box as just part of an infinite bulk material, then I should be able to take the cutoff radius as large as I like, no matter how many images of an atom are seen.


texts: If I conducted 6 trials for a lab, all with the uncertainty of (+/- 0.1 mL)... After averaging the 6 trials to plot the results, what is the new uncertainty?


texts:
I'm continuing with my electrolysis experiments. Over a long time, I seek a perfect electrodes. It seems, that when you pick the right anode and cathode, it might be a lot cheaper than universal super-electrode.

The cathodes are usually OK, since (+) ions do not hurt metals. However, $\ce{O-}$ and $\ce{Cl-}$ are both very agresive and will, sooner or later, destroy any anode I found so far.

My latest experiment was Zinc. Zinc is often used as non-corrosive layer added on iron via electro-plating. So I used it as an anode in $\ce{NaCL}$ aqueous solution. The anode I used was a piece of iron plated with zinc layer.

This scary jelly is forming on it. I also do not see any bubbles at all coming from the electrode - which mean that both chloride and oxygen ions are reacting.

The anode is consumed during the process - but what is produced? The jelly does not burn. When heated intensively, it bubbles and smells like chlorine. Does it decompose?

The orange colour is caused by the iron centre of the anode being oxidized. I tried other pieces of zinc I could find - they all produced this jelly.

Keep in mind, that solution does contain following additional compounds formed from salt and water:

$\ce{NaOH}$
$\ce{HCl}$
$\ce{Cl2}$


texts: Am I understanding buffering capacity against strong acid/base correctly?

texts:
I just want to make sure I'm understanding buffering capacity correctly.

I've been working on this problem:

  Suppose you have an acetic acid buffer, $\mathrm{p}K_\mathrm{a} = 4.74$, at the following $\mathrm{pH}$:

  1) $\mathrm{pH} = 4.00$

  2) $\mathrm{pH} = 4.35$

  3) $\mathrm{pH} = 4.70$

  4) $\mathrm{pH} = 5.00$

  5) $\mathrm{pH} = 5.40$

  6) $\mathrm{pH} = 5.60$

  Which buffer solution will have the highest buffering capacity against $\ce{HCl}$? Against $\ce{NaOH}$ ? Which is the best optimal buffer?

From what I understand, optimal buffers are where $\mathrm{pH} = \mathrm{p}K_\mathrm{a}$, since that is when the ratio between conjugate base and acid is equal to $1$. This means that there is just enough acid/base relative to each other to minimize $\mathrm{pH}$ changes whether a strong acid or base is added.

As for buffering against $\ce{HCl}$, we would want our $\mathrm{pH}$ to be as high as possible, right?

We want as much conjugate base as possible in our buffer to react with the $\ce{HCl}$, while minimizing the changes to the acid, which means we want $\frac{[\ce{A-}]}{[\ce{HA}]}$ to be as high as possible. Maximizing $\frac{[\ce{A-}]}{[\ce{HA}]}$ means $\log \left(\frac{[\ce{A-}]}{[\ce{HA}]}\right) \rightarrow \infty$, which means $\mathrm{pH} \rightarrow 14$, since $\mathrm{pH} = \mathrm{p}K_\mathrm{a} + \log \left(\frac{[\ce{A-}]}{[\ce{HA}]}\right)$.

The explanation for $\ce{NaOH}$ would be the exact opposite. You want as much acid compared to conjugate base as possible so that the acid reacts with $\ce{NaOH}$ while minimizing changes to the conjugate base, which means $\frac{[\ce{A-}]}{[\ce{HA}]} \rightarrow 0$, $\log \left(\frac{[\ce{A-}]}{[\ce{HA}]}\right) \rightarrow -\infty$, and $\mathrm{pH} \rightarrow 0$.

Is my understanding correct? The thing that's tripping me up is that I was told the exact amount of conjugate base and acid is more important than the ratio (e.g., $0.5 / 0.9$ is better than $0.05 / 0.09$), but since there's no mention of exact concentrations in the problem, I'm guessing we just assume that we have sufficient amounts of $\ce{A-}$ and $\ce{HA}$.

Is this generalization correct: if my buffer $\mathrm{pH} <<< \mathrm{p}K_\mathrm{a}$, then does that mean it is optimal against strong bases (and vice versa)?

Thank you for your help.


texts: How to calculate entropy change for a gas reaction using $S^\circ$?

texts:
I'm calculating molar changes in thermodynamic properties due to reactions between gasses (assumed to be ideal gases).  I can calculate $\Delta H$ easily enough, because it's just $\sum_i \nu_i\Delta_f H^\circ_i$, with $\nu_i$ the stoichiometric coefficients. $\Delta G$ (at standard pressure) can be calculated from $\sum_i \nu_i\mu_i$, with $\mu_i = \Delta_f G^\circ_i + RT\log[i]$. Since $\Delta G = \Delta H - T\Delta S$, I can calculate $\Delta S$ as $\frac{1}{T}(\Delta H - \Delta G)$.

So far so good. But I'm inexperienced in working with tabulated quantities (I'm a more of a theoretical physicist than a chemist) and keep making mistakes with signs and units. So I figured that as a sanity check I would calculate $\Delta S$ directly, using tabulated values of $S^\circ$. But then I realised I don't know how to do this, and it seems that none of the textbooks on my desk explain it either.

Based mostly on intuition, it seems like it should be $\Delta S = \sum_i\nu_i(S^\circ_i + R\log[i])$, with the $R\log[i]$ term having something to do with the entropy of mixing. For the example reaction I chose, this gave something with the approximately correct magnitude but the wrong sign (-15.6 instead of 14.2, which is what I get by calculating it from the Gibbs energy and the enthalpy).

So my question is, what is the correct way to calculate the entropy change due to an ideal gas reaction if, for some reason, you only have access to the concentrations and the standard entropies of the reactants?


texts: At what temperature does carbon dioxide decompose into carbon and oxygen?

texts:
If you were to super-heat a mole of carbon dioxide gas, at what point would it decompose into carbon and oxygen? If it decomposes into carbon monoxide and oxygen, at what point do those products decompose? I'm interested in the process from a hypothetical perspective, so energy is not a concern, nor is industrial feasibility.

I'm looking for the heat required for carbon dioxide to break down into atomic carbon and oxygen, if carbon monoxide is being formed then its not hot enough yet!


texts: Universal symbols for molar mass, molarity, and molality

texts:
This is a really basic (perhaps trivial) question, but I just want to confirm:
What are the SI symbols for molar mass, molarity, and molality? For molality and molarity, there is a difference, but I’ve found that the symbol is the same for molarity and molar mass, i.e. M (a big m).
Also, what are the meaningful differences between molarity and molality? Does it just have to do with mass (i.e. difference in mass between solute and solvent) vs. concentration (i.e. within the solution)?
I get the sense that molarity is defunct? I read this here -
https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-8