texts: Is turpentine (as a solvent in plant-based paints) toxic after application? How long?

texts:
Turpentine is often used as a solvent in plant-based paints. It is believed that
turpentine is equally if not more toxic than white spirit (see Green Building Handbook. Volume 1 by Tom Woolley,Sam Kimmins, Paul Harrison and Rob Harrison. p.229). Is it toxic after paint application and for how long?

Updated:
I believe that question can be divided on two simpler subproblems (it's worth to consider them together):

what is the speed of turpentine level reduction in regular environmental conditions? As function of time in analytical form or better graphical curve.
determination of the safe level of turpentine in room according to some authoritative standard. This level likely is disputable, so knowing the speed will help - maybe waiting some additional time (a couple of months) before starting to settle in the room will eliminate the risk completely.


texts: Is there an iron–iron bond in diiron nonacarbonyl?

texts:
Diiron nonacarbonyl, $\ce{[Fe2(CO)9]}$, is often depicted with an Fe–Fe bond as shown at the left-hand side:

The Fe—Fe bond is usually invoked in order to (1) explain the observed diamagnetism and (2) satisfy the 18-electron rule. However, I'm also aware that the presence of such a bond has been challenged numerous times in some textbooks and also by theoretical studies. Being untrained in computational chemistry, though, means I don't fully understand some of these papers.

So: is there a bond? If there isn't (which seems to be the case), can the bonding in this complex still be reconciled with the 18-electron rule?

I'd especially appreciate it if answers include some explanation of what is going on in the literature.


texts: Why do the left- and right-handed enantiomers of a chiral molecule react differently?

texts: So I was researching about thalidomide when a thought struck to me. Why does the left enantiomer react differently than the right? They have the same elements and structure.


texts: Will magnesium undergo a redox reaction with zinc(II) or copper(II)?

texts:
Magnesium can do a redox reaction with $\ce{Cu^2+}$ as well as with $\ce{Zn^2+}$, since Mg has the lowest reduction potential $E_0$. (I am aware that a reaction may or may not be feasible as redox, and this is according the reduction potential of the two half-equations)

\begin{array}{l|l|r}
\ce{Cu^2+ & Cu} &\pu{0.34 V} \\
\ce{Zn^2+ & Zn} &\pu{-0.76 V} \\
\ce{Mg^2+ & Mg} &\pu{-2.37V} \\
\end{array}

I'm supposing we have in one beaker, a solution of $\ce{Cu^2+}$ ions and $\ce{Zn^2+}$ ions and a piece of magnesium. So the possible reactants are: $\ce{Cu^2+}$, $\ce{Zn^2+}$, and $\ce{Mg}$.

The potential difference between $\ce{Mg}$ and $\ce{Cu^2+}$ is greater than with $\ce{Zn^2+}$.
So what's the answer?

My guess is "with $\ce{Zn^2+}$", since by comparing with another example, ethanol ($\ce{CH3CH2OH}$) reduces $\ce{MnO4-}$ to give $\ce{CH3CHO}$ instead of $\ce{CH3COOH}$, if the quantity of $\ce{MnO4-}$ was limited.
\begin{array}{l|l|r}
\ce{MnO4- & Mn^2+}     & \pu{1.51 V} \\
\ce{CH3CHO & CH3CH2OH} & \pu{0.19 V} \\
\ce{CH3COOH & CH3CH2OH}& \pu{0.05 V}
\end{array}

So $\ce{CH3CH2OH}$ reacted with $\ce{MnO4-}$ to give $\ce{CH3CHO}$, that leads me to deduce that in the case of multiple possibilities (i.e. feasible redox reactions), the reaction with the least potential difference takes place (since $1.51 − 0.19 < 1.51 − 0.05$).

From another hand, I guess it's familiar that the other option of having $\ce{Mn^2+}$ reacting with $\ce{Mg}$ is true as being held between the most oxidant which is $\ce{Mn^2+}$ and the most reductant which is solely $\ce{Mg}$ in our case.


texts: Using results of current experiments in silanization, how to achieve a higher contact angle?

texts:
I've done several silanization tests with different solutions and here is a brief of my results:

DichloroDimethylSilan: Advancing=90, Receding=56

ChloroTrimethylSilan: Adv=91, Rec=70

OctaDecylTrichloroSilan: Adv=108, Rec=90

TetraEthoxySilan: Adv=90, Rec=44

OctaDecylTrichloroSilan+ChloroTrimethylSilan(50%): Adv=89, Rec=74

I didn't dilute any of the above solutions and since I want to achieve Maximum Hydrophobicity I gave enough time (~20 min) to all the above reaction to become fully completed.

I'm wondering whether its possible to get a contact angle higher than 108 that I have now. Please let me know what changes should I made? (any pre-treatment of glass before silanizing, any other solutions, etc.)


texts: Could a non-spontaneous reaction occur "on its own"?

texts:
Does spontaneity really only apply to the net free energy change of a reaction?

I used to be taught that spontaneous reactions could occur on their own BUT without enzymes or a spark they might take thousands of years to occur.

So teachers would say that spontaneity is more describing whether a reaction will occur on its own. Rather than a statement of reaction speed.

Because there is still activation energy to deal with, so technically spontaneous reactions to need an input of energy.

So is a spontaneous reaction more a statement of the reaction energetics?

And could a non-spontaneous reaction occur on its own given enough time?


texts:
I am stuck on 2 problems and would be grateful if anyone decided to give me a proper explanation as to how to solve them. I am not sure how to use the given information to correctly solve what is being asked. I have included the answers so its not a matter of academic integrity, I am genuinely lost.

  Given the equation:
  $$\ce{2X^3+ + 3 Y -> 3 Y^2+ + 2X}$$
  The standard reduction potential for the X cation is $\pu{0.498 V}$.
  The standard reduction potential for the Y cation is $\pu{0.187 V}$.
  Using the Nernst equation, calculate the $\log$ of the equilibrium constant $K$ for the above reaction.

The answer is $\log K = 31.52$.

Using the answer, I attempted to work backwards:

$$0.685 = \frac{0.0592}{n} \times 31.52 \implies n = 2.724 ,$$

which I don't understand since $n$ is supposed to be the number of electrons.

  Given the equation:
  $$\ce{2 X+ + Y -> Y^2+ + 2 X}$$
  The equilibrium constant for the reaction is $5.912 \cdot 10^{13}$.
  You measure the concentration of $\ce{Y^2+}$ to be $\pu{0.0674 M}$.
  Calculate molar concentration of $\ce{X^+}$.

The answer is $\pu{33.8 nM}$. This one I'm not even sure.


texts:
I would like to ask a question about Sulfur in the reaction with Nitric Acid, $\ce{HNO3}$ to produce Sulfuric Acid, $\ce{H2SO4}$

I read that as Nitrogen and Sulfur are reduced and oxidised respectively, the reaction equation can be constructed as follows:

$\ce{S + 6HNO3 -> H2SO4 + 6NO2 + 2H2O}$

Now, when I read an article on wikipedia regarding sulfur, the introductory paragraph states the following:

  Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula $\ce{S8}$.

So why is sulfur represented in the equation as $\ce{S}$ and not $\ce{S8}$?


texts: Why HF is said to be formed from H-1s and F-2pz overlap?

texts:
According to Wikipedia, HF is formed by the interaction between hydrogen's $1\mathrm{s}$ orbital and fluoride’s $2\mathrm{p}_z$ orbital:

  In hydrogen fluoride HF overlap between the H 1s and F 2s orbitals is
  allowed by symmetry but the difference in energy between the two
  atomic orbitals prevents them from interacting to create a molecular
  orbital. Overlap between the H 1s and F 2pz orbitals is also symmetry
  allowed, and these two atomic orbitals have a small energy separation.
  Thus, they interact, leading to creation of σ and σ* MOs and a
  molecule with a bond order of 1.

So:

If there is a too large energy separation between H-1s and F-2s, isn't the energy separation between H-1s and F-2p even larger?
Can it be experimentally verified that the bonding is indeed via the F-2p and not the F-2s?


texts: Why proton concentration is divided by 10⁻⁷?

texts: I am reviewing the book Biochemistry Concepts and Connections by Appling, Cahill, and Mathews and I cannot understand why they divide by the hydrogen concentration by $10^{-7}$.  Why not just leave it at the antilog(-8.1) over $\pu{1 M}$ like the other concentrations? I literally have see nothing else on the internet like this.


texts:
I named Citric acid : "3-hydroxypentan-1,3,5-trioic acid"
but when I searched , I found that the right name is "3-carboxy-3-hydroxypentane-1,5-dioic acid"

Can anyone explain to me why my nomenclature is wrong?


texts:
The interatomic distances in $\ce{H2}$ and $\ce{Cl2}$ are $74$ and $\pu{198 pm},$ respectively. Find the bond length of $\ce{HCl}.$
a. $\pu{136 pm}$
b. $>\pu{136 pm}$
c. $<\pu{136 pm}$

According to me, if $\ce{HCl}$ was a non polar molecule then the bond length would simply be
$$\frac{\pu{74 pm} + \pu{198 pm}}{2} = \pu{136 pm}$$
But as there is polarity the electrostatic force of attraction should reduce the bond length to less than $\pu{136 pm}.$
However, the answer is exactly $\pu{136 pm}.$ I do not understand why.


texts: Making benzoyl chloride - yellow liquid and a precipitate?

texts:
I am attempting to produce benzoyl chloride from benzoic acid (I need to convert an isotopically labeled version, so I can't just buy the acyl chloride). I am reacting benzoic acid with excess oxalyl chloride in DCM, and the reaction looks like its proceeding quantitatively, but when I try to rotovap off everything except the product my solution turns pale yellow and I get a white solid.

Both the yellow liquid and white solid appear identical on TLC, and the NMR is consistent with benzoyl chloride, but the physical appearance doesn't seem to match.

Can anyone suggest what might be going on?


texts: Atomic radius and nuclear effective charge in a group

texts: Why even though the effective nuclear charge increases in gruop from top to bottom , the atomic radius increases too? Shouldn’t it decrease with more effective charge on valance electrons and eventually more force affecting them?


texts: As you heat up a substance will it's bonds begin to dissipate?

texts: As you heat something up does it slowly start to dissipate? Water, for instance, boils at 100 degrees Celsius, but if you are heating it up at 90 degrees will its bonds be weaker?


texts: Relationship between molecularity and the reaction order

texts:
Should the molecularity be equal or less than the reaction order?
Consider the reaction:
$$\ce{H2(g) + I2(g) → 2 HI(g)}$$
If we consider the mechanism of this multi-step reaction, the molecularity is 3 (termolecular reaction):
$$
\begin{align}
\ce{I2(g) &<=> 2I(g)} &\quad&\text{(equilibrium reaction)} \\
\ce{2I(g) + H2(g) &-> 2HI(g)} &\quad&\text{(rate-determining step)}
\end{align}
$$
The rate equation for the reaction is
$$\mathrm{rate} = k[\ce{H2(g)}][\ce{I2(g)}].$$
The order of the reaction is 2 here. The molecularity is greater than the reaction order. Is it possible?
Or is the actual mechanism for the above reaction is different?


texts: When the present state of knowledge concerning central noradrenergic transmission was established?

texts:
Some time ago I began to search for descriptions of the mechanisms responsible for the regulation of noradrenergic transmission in the central nervous system of man and to my great surprise the most recent relevant publication I found in periodic literature was published in 2004 (by Eisenhofer, G. et al) and reviewed metabolism of noradrenaline and other catecholamines only.

A bibliography appeared in 2012 under the title "Catecholamine Research in the 21st Century" "provides a guide to the diverse catecholamine research efforts across key themes including, Synthesis and Storage, Release and Re-uptake, Metabolism, Catecholamine Receptors and Catecholaminergic Signaling", but is it a review of the findings latest for the present moment?

I tried to find out looking for books published since 2012 reviewing neurochemistry, neurophysiology, neurobiology, mathematical and computational modelling with application to neuroscience and examining their contents did not find anything like a comprehensive review of the chemistry of noradrenaline.

For comparison a number of such reviews were dedicated to the chemistry of dopamine. An article authored by Meiser, J. et al. is "looking at DA biosynthesis, sequestration, degradation and oxidation chemistry at the metabolic level, as well as at the transcriptional, translational and posttranslational regulation of all enzymes involved. This is followed by a short overview of cellular models currently used in Parkinson's disease research".

Alternative models were provided in the following publications:

Best, J. A., Nijhout, H. F., & Reed, M. C. (2009). Homeostatic mechanisms in dopamine synthesis and release: a mathematical model. Theoretical biology & medical modelling, 6, 21. doi:10.1186/1742-4682-6-21

Qi, Z., Miller, G. W., & Voit, E. O. (2008). Computational systems analysis of dopamine metabolism. PloS one, 3(6), e2444. doi:10.1371/journal.pone.0002444

A mathematical model of serotonin synthesis, release and reuptake was also created:

Best, J., Nijhout, H. F., & Reed, M. (2010). Serotonin synthesis, release and reuptake in terminals: a mathematical model. Theoretical biology & medical modelling, 7, 34. doi:10.1186/1742-4682-7-34

Can anyone provide an authoritative commentary to the picture outlined above?

References:

Eisenhofer, G., Kopin, I. J., & Goldstein, D. S. (2004). Catecholamine metabolism: a contemporary view with implications for physiology and medicine. Pharmacological reviews, 56(3), 331-349.

Eiden, L. E. (Ed.). (2013). Catecholamine Research in the 21st Century: Abstracts and Graphical Abstracts, 10th International Catecholamine Symposium, 2012. Elsevier.

Meiser, J., Weindl, D., & Hiller, K. (2013). Complexity of dopamine metabolism. Cell communication and signaling : CCS, 11(1), 34. doi:10.1186/1478-811X-11-34


texts: Why are smoke odors persistent in fabrics?

texts:
Obviously smoke is very complex, but apparently phenol compounds are the main components of wood smoke that produce the characteristic odor.  (One of more significant of these compounds seems to be syringol.)  The human nose seems to be pretty sensitive to these compounds.

Smoke seems to be very easily absorbed by various fabric-like materials, which then release the compounds back into the air over long periods of time, making the odor quite persistent.  I'd like to know what is going on with these compounds and the fabric-like materials to cause this behavior.


texts:
In the following homework problem, the answer says:

"$E ^{o}_{cell}$ is negative, which makes the $\ce{Fe}$ and $\ce{Ga}$ half-reactions non-spontaneous."

But I found $E ^{o}_{cell}$ to be positive - NOT negative:

$$E ^{o}_{cell} = E ^{o}_{cathode} -E ^{o}_{anode} =
E ^{o}_{Fe} - E ^{o}_{Ga} = -0.409\,\mathrm{V} - (-0.56\,\mathrm{V}) = +0.151\,\mathrm{V}$$

which means that these half-reactions would actually be spontaneous.

Am I solving this problem wrong or did the writer of this question make a mistake?

After all, $\ce{Fe}$ should be the cathode since it has a more positive voltage. Right?


texts: Direction of gas molecules in kinetic model of gases?

texts:
So when learning about the kinetic model of gases, my teacher said that in a volume $A*v_{x}*\Delta t$, exactly half the molecules will have a velocity component of $v_x$ and the other half will have a velocity component of $-v_x$. But I think they are wrong!

Because there should be some small portion of gas molecules that will have a velocity component of: $v_x = 0$

Am I correct? So is the term for the average number of collisions with the wall during the time interval $\Delta t$, just an approximation?:

$(0.5)*A*v_{x}*\Delta t*n*N_a/V$

This is clear with an example. If there are three molecules in a container, one moving left on the x axis, one moving right on the x axis, and one moving directly up the y axis,  then on average, only 1/3 of the molecules is moving towards the right wall.


texts:
I'm currently looking at a problem that asks about the structural relationship between the 4 nitrogens the caffeine molecule. I am asked to identify whether they are in perpendicular planar, coplanar, or inverted planar formations.

I'm am a bit lost as to how I should approach this problem. Should I look at hybridization (3 Ns are sp3, 1 N is sp2)? Or resonance (seems that all Ns are involved in resonance)? Or should I be concerned with sterics?

Lastly, what are some examples that might assume a perpendicular planar, coplanar, and inverted planar formation? I don't think I've ever seen such shapes before...

Would someone please point me to the right direction?


texts: How to round significant figures correctly?

texts:
Calculate how many grams of p-nitrophenol are required to prepare $\pu{250 mL}$ of a $\pu{11 mM}$ solution. (Answer to 3 significant figures.)

I worked it out as

\begin{align}
\frac{250}{1000}\,\mathrm{L} \times (\pu{11E-3 M}) \times \pu{139.11 g//mol}
  &= \pu{2.75E-3 mol} \times \pu{139.11 g//mol} \\
  &= \pu{0.3825525 g}
\end{align}

Is that $\pu{0.383 g}$ or $\pu{0.382 g}$ when approximated to 3 significant figures?
I think it is $\pu{0.383 g}$, but that's only going by the general rule of "up" approximating a five.


texts: How to set up an ICE table for adding a weak acid to a strong acid

texts:
I am working on setting up an ICE table for adding 0.020 mol HCl to 1.0 L of 0.10 M propanoic acid.  Since these are both acids (propanoic acid being the weaker one and HCl being strong), how would I set this up in an ICE table to calculate the pH of the resulting acid?
Edit: I was able to find an answer by taking the negative log of 0.02 to get the pH (because HCl is a strong acid).  However, I am unaware with how to even set up the ICE table.


texts:
This question was given by my teacher in class:

  Draw the structure of 2,3-diethylheptane.

So I drew the following:

But now if I name the compound according to the longest chain, it comes out to be 3-methyl-4-ethyloctane! How can I properly draw these structures?


texts: Function of 'organic' vs regular pipe cleaner

texts:
Recently, I needed to buy some pipe cleaner, as sometimes even with care hair and other detritus gets lodged so deep down the shower drain that it is not possible to get it out. I always try to avoid/reduce use of bleach and other hard chemicals or products that incorporate them, as in the end it goes down the drain is not good for the environment.

However, unfortunately the 'bio' product of the same brand of cleaner I had used before (didn't know it existed before) was not very satisfactory so far. Is there maybe someone here who could offer details of the chemical function of these types of cleaners, and either knows a method to improve the use of the bio/organic one or recommend another product or compound that is easy on the environment but cleans drains well? For the proper use, the instructions say that for the 'organic' one (yes sorry for that chemically improper use but ...) you should add hot or warm water to start the reaction, though my worry is also that this added water will just flush the product down the drain depending on the size of the drain.

I know some of these ingredients and how they likely function, but not all of them and I am not sure what the combined effects might be. To my understanding the 'non-organic' one relies on the reactive power of chlor(ide/ine) and resulting reaction products, whereas with the organic one I am not really sure.

Specifically, it is about these two products:
rorax and rorax bio (at least on the German market)
The ingredients of rorax (said to be chlorine based in marketing) are given as water, sodium hydroxide, sodium hypochlorite, myristamin oxide, sodium silicate, fatty acids, C6-12-, natrium salts as per http://detvo.werner-mertz.de/?lang=de&country=DE&prod_id=109655

The ingredients of rorax bio are given as water, sodium chloride, urea, sodim laureth sulfate, sodium thioglycolate, sodium hydroxide, Amide polyglycol ether, parfum, colorant
according to http://detvo.werner-mertz.de/?lang=de&country=DE&prod_id=114331


texts: What is the reason of the color difference for the cis/trans isomers of tetraamminedichloridocobalt(III) chloride?

texts:
The cis and trans isomers of $\ce{[CoCl2(NH3)4]Cl}$ are quite famous as one is purple and the other one is green which is a huge difference in color. Now I can't find any information to why this is the case?

I remember they told me in the lecture on organometallic chemistry when we were discussing substituted carbonylmetallates that a trans-effect occurs where a π-donor trans to the carbonyl (which binds to the metal's d-Orbitals via its antibonding π*-orbitals) increases the electron density in the metal and therefore also increases the the bond's strength ($\ce{M-CO}$) which then changes the bond length. A π-acceptor ligand on the other hand decreases the e-density.

In case of an octahedron the trans isomer would only possess same ligands trans positioned to each other while the cis isomer has mixed ones, too.

But is this the explanation I am looking for or is there another effect I just can't think of right now?


texts: For the H NMR of the compound I am wondering why peak (A) is the farthest out of all of them? I think that it is due to the electro negativity of oxygen. Am I correct? If so, why would the presence of oxygen push the peak to the left?


texts: Index of Hydrogen Deficiency for para-Toluenesulfonylchloride

texts:
In para-Toluenesulfonylchloride, there are 5 pi bonds and 1 ring. This suggests a IHD of 6. However, the actual IHD is 4. How come?

Is it because the formula IHD = rings + pi bonds does not apply to compounds containing sulfur? If not, what formula do I use? I have this formula:

$IHD = \frac{2C + N - X - H + 2}{2}$

Using this formula yields a IHD of 4.


texts: Demonstrating orthonormality for wave functions for ground state and excited state of He

texts:
The electron configuration of the ground state $\ce{He}$ atom is $\ce{1s^2}$, and the excited state configuration under study is $\ce{1s^2 2s^1}$. Show that these states are orthonormal, i.e.,

  $$\langle\Psi_0 \vert\Psi_0\rangle = 1$$

  $$\langle\Psi_1 \vert\Psi_1\rangle = 1$$

  $$\langle\Psi_0 \vert\Psi_1\rangle = 0$$

I start off by defining the wave functions as Slater determinants,

$$
\Psi_0 = \frac{1}{\sqrt{2}}
\begin{vmatrix}
\phi_1(1)\alpha(1) & \phi_1(1)\beta(1) \\
\phi_1(2)\alpha(2) & \phi_1(2)\beta(2)
\end{vmatrix}
$$

$$
\Psi_1 = \frac{1}{\sqrt{2}}
\begin{vmatrix}
\phi_1(1)\alpha(1) & \phi_2(1)\beta(1) \\
\phi_1(2)\alpha(2) & \phi_2(2)\beta(2)
\end{vmatrix}
$$

I am able to show that the wave functions are normalized, but I have trouble showing that they are also orthogonal. I get that $\langle\Psi_0 \vert\Psi_1\rangle = 1$. I set up the integral over all coordinates, carry out the multiplications, and add together the terms that are equivalent due to indistinguishable electrons (identical when all coordinates are interchanged). I end up with the expression

$$
\int d\tau \left[  \phi_1^*(1)\alpha(1)\phi_2^*(2)\beta(2)\phi_1(1)\alpha(1)\phi_2(2)\beta(2) - \phi_1^*(1)\alpha(1)\phi_2^*(2)\beta(2)\phi_1(2)\alpha(2)\phi_2(1)\beta(1)   \right]
$$

where $d\tau$ represents all coordinates. Separating the spin coordinates from the spatial coordinates, I get that

$$
\langle\Psi_0 \vert\Psi_1\rangle = \\
\sum_{m_{s1}=-1/2}^{1/2} \sum_{m_{s2}=-1/2}^{1/2} \alpha(1)\alpha(1)\beta(2)\beta(2) \cdot \langle\phi_1(1) \vert\phi_1(1)\rangle \cdot \langle\phi_2(2) \vert\phi_2(2)\rangle \\
- \sum_{m_{s1}=-1/2}^{1/2} \sum_{m_{s2}=-1/2}^{1/2} \alpha(1)\alpha(2)\beta(2)\beta(1) \cdot \langle\phi_1(1) \vert\phi_2(1)\rangle \cdot \langle\phi_2(2) \vert\phi_1(2)\rangle \\
= 1 - 0 = 1
$$

The first term reduces to $1$, I find, while the second term reduces to $0$. To get $\langle\Psi_0 \vert\Psi_1\rangle = 0$, either both terms need to be $1$, or both terms need to be $0$. Something must be incorrect. Is there some obvious flaw in my derivations?


texts: Chemical bond at Aluminum / Aluminum oxide interface

texts: I am trying to find out what chemical bond holds aluminum oxide to the aluminum on which it forms. The only information I was able to find on the internet was in a Google book which suggested that the bond was ionic in nature.


texts: where is sulphate going here? electrolysis of magnesium sulphate

texts:
I am electrolyzing a water + magnesium sulphate solution using copper for both electrodes. I am getting a light-blue precipitate forming which I believe to be a mixture of copper hydroxide and magnesium hydroxide, which are both poorly soluble. The solution is remaining clear which tells me that basically no copper sulphate is forming.

My question is, where is the sulphur from the sulphate going?

The mixture is not becoming acidic as if sulphuric acid was forming, and I do not detect any smell of sulphur is if some sulphur oxides were being released as gas.


texts: Examples of intramolecular hydrogen bonding closing bond angles

texts:
Okay, we've established that intramolecular hydrogen bonding can exist in molecules, and doesn't always serve the purpose of closing the bond angle at least relative to other stereoisomers of the same compound.

Consider nitrous acid and its cis and trans configuration; hydrogen bonding is only a possibility in the cis configuration, yet the cis conformation has (rather unexpectedly) a larger bond angle than in the trans conformation. The same goes for nitric acid.

Why does nitrous acid exhibit (unexpectedly) different bond angles?

So, are there actually any examples of molecules in which internal hydrogen bonding serves the purpose of closing up the bond angle relative to other conformations of the same molecule?


texts: Why do we subtract the mass of one proton in mass spectrometry (negative mode)?

texts:
This is probably very basic, but I have been given the understanding that we subtract the mass of only one proton when looking for our compound in a mass spectrometry (negative mode). I dont really understand why we are only subtracting the mass of one proton when our compound could potentially loose more than one proton at higher pH?

In example, the amino acid glutamate, would it not loose or gain more than one proton is a negative (higher pH) or positive (lower pH) mode mass spectrometry (MS)? Perhaps I have misunderstood the concept of negative and positive mode for MS?


texts: Reducible representation of planar molecule N2H2 with bond lengths as a basis

texts:
I'm studying about molecular symmetry and its representations. Today I got a little confused about the planar $\ce{N2H2}$ molecule.

It looks like this

The basis in the example was chosen as $\Delta r_1, \Delta r_2$, i.e. lengths of N-H bonds. Then, it was stated, that the molecule belongs to $\mathrm C_{2h}$ point group, which I agree with.

The problem is, the example stated, that the reducible representation is

\begin{array}{|l|l|l|l|}
\hline
{} & \mathrm E & \mathrm C_2 & i & \sigma_h\\ \hline
\Gamma & 1+1=2 & 0+0=0 & 0+0=0 & 1+1=2\\
\hline
\end{array}

And here I don't understand, what's going on. I understand, that $\mathrm E$ and $\sigma_h$ are 2, as both $\Delta r_1$ and $\Delta r_2$ stay the same after those operations, i.e. bond length doesn't change.

But, bond lengths don't change after $\mathrm C_2$ and $i$ either, so why are there zeros in the table?

I'd understand it if we used vectors of Cartesian coordinates on every atom as a basis, but in this case, I'm quite lost.

Could you, please, explain it to me?

The example is taken from this presentation (slide 18).


texts: Intermolecular forces - Covalent bonding

texts: Im confused. How to relate permanent dipole dipole moment, temporary dipole induced dipole and Van der waals forces of attractrion?


texts: Reaction of H2o2 on Ozone in jar washing Tank in packaged drinking Water Company

texts: What is reaction of H2o2 when added in Jar Washing Tank  where ozone is also being dosed at 0.5ppm in a Packaged Drinking Water Industry ?


texts: I have read that aniline does not undergo Friedel–Crafts reaction because it complexes with Lewis acid $\ce{AlCl3}.$ Will it also react with $\ce{FeBr3}$ during bromination (to receive a 3-bromo substituted benzene)?


texts: What is the crystal structure of ammonium hydrogen sulfate? It's beautifully birefringent

texts:
I make art using a microscope and camera. I have heated ammonium sulphate that decomposes to ammonium hydrogen sulfate, melts, and then recrystalises to produce exceptionally beautiful birefiringent colours.
I am interested in its typical crystaline structure as perhaps other chemicals with similar structure may also be interesting artistically.
I have tried looking it up in ChemSpider, but no luck. I took some university courses in chemistry, so I have some (out of date) chemistry knowledge.


texts: UV-Vis spectra of [Co(H2O)6]^2+ (hexaaquacobalt ion)

texts:
I observe the UV-Vis spectrum of $\ce{[Co(H2O)6]^{2+}}$ and there is a little peak at ~$\pu{640nm}$. By observing the Tanabe-Sugano diagram I see that the spin allowed transitions are:

$\ce{^4T_{1g}(F) → ^4T_{1g}(P)}$

$\ce{^4T_{1g}(F) → ^4A_{2g}}$

$\ce{^4T_{1g}(F) → ^4T_{2g}}$

The answer about why there is this little peak is that it is explained by the $\ce{^4T_{1g}(F) → ^4A_{2g}}$ transition and it has to do with a two-electron transition. I can't understand why it is explained by this transition and also how do I know that it has to do with 2 electrons.


texts: Number of stereoisomers of tetramethylspirononane

texts:
The above compound – 2,3,7,8-tetramethylspiro[4.4]nonane – clearly exhibits both optical and geometrical isomerism. The question is, how many stereoisomers does it have in all?

As the number of possibilities are many, I couldn't really visualise the molecule's all possible stereoisomers properly. Could someone please help me count the total number of stereoisomers?

I figured that the carbon common to both rings is sp3 hybridised (tetrahedral geometry), and the two rings don't lie in the same plane.


texts: How can compounds like XeO4 form tetrahedral structures despite having double bonds?

texts: Xenon tetroxide is tetrahedral despite having double bonds. Is it something to do with $d$ orbitals? Also things like sulfur trioxide (trigonal planar with three double bonds but the sulfur is hypervalent). Is it possible for the $\pi$ bond to be formed from overlap of $d$ orbitals from the central atom with $p$ orbitals of the oxygen?


texts: Chemoselectivity in synthesis of paracetamol

texts: In the reaction below, why does acetic anhydride not react with the -OH group to form an ester instead?


texts: What materials reversibly swell up slightly when in a moist environment?

texts:
I am aware that some "Super Absorbent Polymers" can swell up enormously when they absorb water. However, I am looking for a material which swells up (maybe about 30% to 100%) when in a moist environment, and which will contract again when moved to a less moist environment.

I.E. by measuring the expansion of the material, one could determine the moisture content of the environment the material was in. It would act like a moisture measurement device.

Are there any such materials? Perhaps there are some "Fairly Absorbent Polymers"


texts: Has this way of comparing internal energy got any sense?

texts:
Can internal energy between molecules be compared?
For example, $\ce{H2}$, $\ce{O2}$ and $\ce{N2}$ have some internal energy ($U$) but taking infinite distance between atoms as zero. But each reference point is different. So, can $U$ for those molecules be compared?


texts: What is the actual density of CAS 7647-14-5 (NaCl, 99+%)?

texts:
I'm not a chemist by profession, so please forgive any syntactical or vernacular oversights on my part.  Basically, I'm getting mixed messages from different sites about the density of sodium chloride. Wikipedia and some other sites list the density as $2.16$ or $\pu{2.17g/cm^3}$, while other sites list it as $\pu{1.199g/ml}$.  Paradoxically, this one lists it as both:

https://www.bio-world.com/productinfo/4_847_63_473/9221/Sodium-chloride.html

Would someone be kind enough to point out what I am missing, please?  I have reagent-grade NaCl that I need to measure accurately in order to obtain a correct weight/volume percentage.  Thanks


texts: Physical significance of magnitude of ΔG (change in Gibbs free energy) of a reaction

texts:
In thermodynamics, we know that if $\Delta G$ of a reaction is negative, the reaction is spontaneous.
Suppose we are given with two spontaneous reactions ($\Delta G\lt0$) with corresponding magnitudes of $\Delta G$. Can we extract any other information from these magnitudes?


texts: Diffusion Phenomena : Why does diffusion occur?

texts: Why do things diffuse that is why do they go from a place of higher concentration to a place of lower concentration?


texts: How do you connect a battery to a galvanic cell in order to reverse the flow of electrons?

texts:
Assume you have a galvanic (voltaic) cell with E = +2V. If you wanted to reverse the current by inserting a 9V battery, which end of the battery should connect to the cathode of the galvanic cell?
The Kaplan answer key states that the "positive end of the battery should connect to the cathode."
Since electrons flow from anode to cathode in the galvanic cell, we want them to flow from cathode to anode to reverse the current. In a battery, electrons move from the negative to positive end. Therefore, why wouldn't the positive end of the battery be on the galvanic cell's anode to attract electrons in order to reverse the current?
Could someone point out the flaw in my reasoning?
Thanks :)


texts: What is the difference between $$\Delta Q$$ and $$\mathrm dQ$$ in thermodynamics? I think one is used when the change is very small and the other with bigger changes, but I am not sure.


texts: Why do some elements such as polonium not follow the trend of decreasing atomic radius?

texts: Most of the periodic table follows the trend of increasing radius as you move down a family and decreasing radius as you move across a period. Why is this trend not observed for polonium?


texts: What is behind of the attraction between a burned matchstick with a magnet?

texts:
I do not know how to understand the reasons of why a burned matchstick is attracted by a magnet (most probably) of Neodymium.

Here are some screenshots of a video in which this natural phenomenon is presented:

(In the video, see at 1 min 25 s):

Source
Source


texts: Steric hindrance of an unbonded electron pair

texts:
This question is half inspired by this question, and half inspired by the structure of molecules like hydrazine and hydrogen peroxide.

When I was looking at the aforementioned molecules, I started trying to reason as to why the lowest energy conformation of these molecules are what they are.

$\hspace{34ex}$

In hydrazine, the lowest energy conformation is not the one in which the unbonded electron pairs are anti-periplanar. This makes me think that hydrogen have a greater steric hindrance than unbonded electron pairs do.

$\hspace{34ex}$

In hydrogen peroxide, however, the lowest energy conformation is not the one in which the hydrogen are anti-periplanar. This contradicts what I reasoned form the structure of hydrazine.

Being confused by this, I tried a different approach—what about the cyclohexyl carbanion? Surely using $\Delta G = -RT \ln{K_\mathrm{eq}}$ the relative steric hindrance of an unbonded electron pair and a hydrogen atom could be determined. What I became unsure about, however, was how rapid inversion might affect this, and additionally whether or not there even is even any data regarding the major and minor confirmations of the cyclohexyl carbanion (because I am unsure if it even exists in such a way that this can even be measured).

So am I flawed in my reasonings? Does the equilibrium data for the cyclohexyl carbanion exist?


texts:
Why do cotton clothes take a long time to dry as compared to synthetic clothes?
I read in a book that cotton fibres form hydrogen bonds with water molecules and thus, the rate of evaporation of water molecules is reduced in the case of cotton clothes. Is that so? How are the synthetic and cotton fibres different chemically? What is the structure of these two fibres like?


texts: How do I go about calculating protein concentration to make a set of protein standards for protein quantification via dot blot?

texts:
I have been given a protein of unknown concentration and have been asked to make a set of standards using a protein with a known concentration so we can quantify roughly via dot blot.

I need to know how to work out the calculation part. I would like to learn both mass and molar.For example, the information I have for my standard protein is it is at a concentration of 30mg/ml and 550uM. I want to put, for example, 1ul dots of this protein on the membrane for my blot. I want several dilutions of my standard, for example ranging from 20pg to 100ng. How do I work it out to get varied concentrations from the stock to my 1ul volumes on my blot?


texts: What happens with sulfur dioxide reacts with dimethyl trisulfide? What compounds are left over?

texts:
I have only found one single reference to this reaction online which states $\ce{SO2}$ will destroy DMTS ($\ce{C2H6S3}$), but I cannot find a reference as to what may be happening or what may be left over.
Can anyone help me solve this? I'm not a scientist or student. I'm actually a home brewer trying to reduce DMTS in a finished beer by potentially adding $\ce{SO2}$, but I don't want worse compounds left over.


texts: How to calculate molar concentration from equilibrium equations with no initial concentration given?

texts:
I have the equations:
\begin{align}
\ce{CO2(g) + H2O(l) &<=> H2CO3(aq)} &\quad K_1 &= 10^{-1.47} \tag{1}\\
\ce{H2CO3(aq) &<=> H+(aq) + HCO3-(aq)} &\quad K_2 &= 10^{-6.35} \tag{2}\\
\ce{HCO3-(aq) &<=> H+(aq) + CO3^{2-}(aq)} &\quad K_3 &= 10^{-10.33} \tag{3}\\
\end{align}
Atmospheric $\ce{CO2}$ is at $\pu{10^{-3.5} atm}$ and the solution is pure water.
So far I have been able to find the equilibrium equations and have got the concentration of $\ce{H2CO3}$ to be $10^{-4.97}.$ However, from this I do not know where to go in order to find the concentration of bicarbonate ($\ce{HCO3-}$).
I have the equilibrium equations as:
\begin{align}
\tag{1}
  \frac{[\ce{H2CO3}]}{[\ce{CO2}][\ce{H2O}]} &=
  K_{\ce{CO2}} = 10^{-1.47}\\
\tag{2}
  \frac{[\ce{H^+}][\ce{HCO3^-}]}{[\ce{H2CO3}]} &=
  K_1 = 10^{-6.35}\\
\tag{3}
  \frac{[\ce{H^+}][\ce{CO3^2-}]}{[\ce{HCO3^-}]} &=
  K_2 = 10^{-10.33}
\end{align}
By multiplying $10^{-1.47}$ by $10^{-3.5}$ I got $10^{-4.97}$ as previously stated.
From there I get $\ce{HCO3-}$ to be $10^{-6.35}+\frac{10^{-4.97}}{\ce{H+}}$.
However I do not know how to find $\ce{H+}$.


texts: How to determine optical activity of a compound without asymmetric carbons theoretically?

texts:
I know that a compound doesn't need to have a chiral carbon to be optically active. So how can I find out whether a compound drawn on paper is chiral without access to any experiments? e.g. 1,2,2-tribromopropane

The question is expected to be solved using only pen and paper


texts:
I have read that vapour pressure of a mixture of two immiscible liquids is
$$P=P^0_A + P^0_B$$ where A and B are immiscible liquids.

If they are immiscible, they would form separate layers. Thus since the more dense liquid would be below the less dense liquid, it would have no interface with the gas phase. Given this lack of an solid-gas interface, should the pressure due to the lower layer be zero?


texts: Old sample of sodium tetraphenylborate—why it is red?

texts: I have a really old sample of sodium tetraphenylborate. It should be white, but it is red. Does anyone know what was formed and how it influences precipitation of cations in water?


texts: What is considered room temperature in Celsius?

texts: Recently, I have seen room temperature listed at 20 °C and 25 °C. Which one is more accurate for use in chemistry problems?


texts: Why replace c with v in Broglie hypothesis

texts:
I am in XI and I am currently studying atomic orbitals, I stumbled up and am stuck at the following step of de Broglie's hypothesis.

I did a little search on-line and found almost same derivation everywhere, the only place I found a more complex and supposedly accurate formula was the Wikipedia itself, though it did not explain the derivation.

Few such sites:

http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/02._Fundamental_Concepts_of_Quantum_Mechanics/De_Broglie_Wavelength
http://entrancechemistry.blogspot.in/2012/09/de-broglie-equation.html

In the derivation of the formula $$\frac{1}{\lambda}=\frac{h}{m\color{green}c}=\frac{h}{m\color{red}v}$$

we replace $c$ with $v$. I want to ask why?

As of Wikipedia it gives a better formula with the Lorentz factor $\gamma$ :-

$$\frac{1}{\lambda}=\frac{h}{\color{red}\gamma m_oc}=\frac{h}{m_ov}  \sqrt{\color{red}1\color{red}-\frac{\color{red}v^\color{red}2}{\color{red}c^\color{red}2}}$$

Can anyone give the derivation or a hint or a logic that helps understand why the derivation from $E=mc^2$ and $E=h\nu$ gives the De Broglie equation.


texts: Boiling and Melting point of Lithium (or any other element that does not occure in free state)

texts:
The melting and boiling point of Lithium as compared to other members of the Alkali group metals is high. But, Lithium does not occur in the free state.

So, what does it mean that it has high melting and boiling point? How are its BP and MP measured if it isn't in the free state?


texts: Why does hydrogen form on such a long time scale?

texts:
If we were trying to figure out the time scale for a gas-phase reaction between two hydrogen atoms in a molecular cloud (which has density $~\pu{10^4cm^-3}$), apparently the reaction would happen on a time scale proportional to the inverse of the density multiplied by $10^{15}$ years.

Aside from the cloud not being dense and the probability that a collision will surpass the activation energy is small, is the time elongated because you need to induce a dipole moment between two hydrogen atoms to actually bind them together?

I recently read somewhere that even if the reactants would go into the unbound state of $\ce{H2}$ they can't emit a photon that would let it go into the bound state of $\ce{H2}$. I guess they are talking about quantum mechanics, but it is not obvious to me what the bound and unbound states of molecular hydrogen are. (If someone could clarify that too)


texts: Solubility in different pressure conditions

texts:
I am working on my scholarship exam practice. I believe this exam assumes high school + first year university knowledge. And I'm not quite sure what I did wrong. Could you please have a look?

  The solubility of oxygen in 1.0 L water is 28 mL at 25 °C and 1.0 atm.
  How much oxygen can be dissolved in 1.0 L of water at 25 °C and 4.0 atm?

The answer remains 28 mL but IMO I thought when pressure goes up 4 times while other factors are constant, the solubility would do that as well. Please help on where I missed and what topics I should focus on specifically.


texts: Is there a chemical treatment that could remove sodium and calcium ions from the surface of soda-lime glass to turn it into quartz glass, increasing the hardness?


texts: What does it mean when "a gas is dilute in CO₂"?

texts:
I'm reading an article about carbon sequestration, and I came across a strange phrase:  "The flue gas is dilute in $\ce{CO2}$".  I can't quite ascertain its meaning from the context.  I think it means that the $\ce{CO2}$ is in low concentration in the flue gas, but I'm no chemistry expert.

Does this have a technical meaning in chemstry when a gas is dilute in another substance?


texts:
We did a lab where we built a simple electrolytic cell. In a beaker was a solution of $\ce{CuSO4}.$ A copper strip (anode) and a copper wire (cathode) was place in it. A wire connected the copper strip to the negative DC power source and a wire connected the copper wire to the positive DC power source. The power source was turned on and the copper wire was electroplated.

Considering that both electrodes are the same material, would it be possible to create a galvanic cell by reversing the reaction?

I think it would not be possible. Since galvanic cells use spontaneous reactions to create electrical energy, you would have these two copper electrodes in a solution of $\ce{CuSO4}$ separated by a salt bridge and connected by a wire. Nothing would happen because both coppers are the same and neither one of them can attract electrons more than the other.


texts: What's the difference between povidone K29/32 and povidone K30?

texts:
I'm specifically looking at the two as inactive ingredients in the drug lamotrigine. How do the povidone K values differ chemically and/or in the context of lamotrigine?

They're obviously designed to be completely inert, but is there any chance they're acting differently in the body?


texts: Are all esterification reactions reversible? What is their general mechanism?

texts: For example the reaction of ethanoic acid with ethanol is reversible, however is this true for all esters? I'm not quite whether it is as easy for a reversible reaction to occur both ways. Is there a limit to the complexity an ester can be? What would be the general mechanism for these reactions? I assume there is no limit on the complexity (carbon chain length) of esters, other than the frequency of longer-chain carboxylic acids and alcohols needed to form them. Is this true?


texts: Why does permanent marker writing come off a white board when coated with white board marker?

texts:
Why is it that dry erase markers allow permanent markings to come off?

Here's a demonstration.


texts: Electrochemistry - Redox & Electroplating

texts:
I've stumbled across an electrochemistry problem that I need help on:

$$\ce{Fe~|~Fe^{+2}~||~Cl^{-},Cl2~|~Pt}$$

I understood that iron is at the anode and is being oxidized, however I do not know what was going on with chlorine, it looks like it is being oxidized while it is supposed to be reduced.
Maybe this is a non-spontaneous reaction? Can this be possible, can chlorine be used as an oxidation reaction? And if so how can we calculate the voltage?


texts: Can an uncharged particle pass through a molecular bond?

texts: Do particles ever pass through or interact with the molecular bond? Is there a physical size limit? What happens to the atoms and the particle and does this ever happen in real life?


texts: Quasi-steady state hypothesis application

texts:
Consider the reaction scheme:

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

where $\ce{S}$ is the substrate, $\ce{E}$ is the enzyme, $\ce{P}$ is the product, $\ce{C1}$ and $\ce{C2}$ are enzyme substrate complexes. Let $[\ce{S}] = s$, $[\ce{E}] = e$, $[\ce{C1}] = c_1$, $[\ce{C2}] = c_2$ and $[\ce{P}] = p$ be the concentrations of each respective chemical. I have simplified this system down to

\begin{align}
\frac{\mathrm ds}{\mathrm dt} &= -k_1se_0 + (k_1-k_3)sc_1 + (k_1s+k_4)c_2 \\
\frac{\mathrm dc_1}{\mathrm dt} &= k_1se_0 - (k_1s+k_2+k_3s)c_1+(k_4-k_1s)c_2 \\
\frac{\mathrm dc_2}{\mathrm dt} &= k_3sc_1-k_4c_2 \\
\end{align}

using the conservation equation $e=e_0-c_1-c_2$. I have found that $p(t) = k_2\int c_1(t) \,\mathrm dt$. Now I need to use the quasi-steady state hypothesis to show that $$\frac{\mathrm ds}{\mathrm dt}= - f(s),\qquad f(s) = \frac{k_1e_0s}{1+\frac{k_1}{k_2}s + \frac{k_1k_3}{k_2k_4}s^2}.$$

Now I'm not really given much information on this hypothesis. I have been told it means

  We assume that the initial stage of complex formation is very fast. After which it is essentially at equilibrium.

So how do I apply the hypothesis to transform $\mathrm ds/\mathrm dt$?


texts: What impact does heating or cooling have on the oxidation reduction potential of water?

texts: There are alkalinizing water ionizers on the market that lower the ORP of water. Does heating or cooling that water have an impact on its ORP?


texts:
A "van't Hoff apparatus" is mentioned as a means of performing a reaction involving gases in a reversible manner, for instance here.

Unfortunately I have been unable to find a description of such a device using a web search (including on this site). It may be that the device has other names. I intuit from the post above that the apparatus is similar to the device used to measure the Joule-Thompson coefficient of a gas.

Could someone provide a description of the nature and operation of such an apparatus (even if it is only a theoretical device)?


texts: Five-pointed crown alkane C25H40: does it exist?

texts:
My 4 year old granddaughter, playing with molecular models, began making a cyclopentane ring, each of whose carbons bore a spiro-connected cyclopentane ring of its own , in the manner of spiro[4.4]nonane.  If she hadn't run out of carbon atoms first, the result would have been a pentagonal crown, with the five outer cyclopentane rings perpendicular to the central one.

I wonder if such an alkane has been synthesized. Its molecular formula would be $\ce{C25H40}$. I can't think of why the molecule would be unstable or sterically impossible, but I couldn't find it in a Google search on $\ce{C25H40}$.

In particular,  I wonder if the five outer rings would be exactly perpendicular to the center one (eclipsed), or somewhat staggered.


texts: Is it more economical to liquify natural gas to ship overseas or convert it to propane (C3H8) and ship it overseas?

texts:
Problem statement: Companies want to frack oil wells and then export natural gas overseas using transport via high pressure pipeline followed by liquefaction at a terminal port.

If the methane component in natural gas ($\ce{CH4}$) can be converted to propane $\ce{C3H8}$, that would leave $\ce{H2}$ which can be combined with nitrogen to create ammonia-based fertilizer.

If the process is done at the well, propane could also be reverse-fed to wells in liquid form to use in place of water for fracking, after which the propane could be drawn off by lowering the pressure (such that it is then in the gas phase) and recompressed to liquid at $160 \ \mathrm{psi}$. This reduce water contamination and propane would not be lost.

In the liquid phase at $160 \ \mathrm{psi}$, propane has a volume $\frac{1}{250}$ as it does in the gas phase, and consequently propane would require a pipeline much smaller than natural gas for same volume sent.

On the receiving end, propane has a higher value for its ease of transport and storage as well as larger consumer base.


texts: "Number of moles of electrons involved in the reaction" for hydrogen cell

texts:
I understand we can calculate the maximum work done by the electromotive force (driving electrons through a cell) by multiplying the potential of the cell with the charge of one mole of electrons (Faraday's constant) and with "the number of moles of electrons involved in the reaction". I thought that in the case of a hydrogen cell: the reaction $\ce{H2 - 2e- -> 2H+}$ involves two electrons but I can see on wikipedia that in the Nernst equation for the standard hydrogen electrode $z$ (the number of moles involved) is considered to be 1.

So what does this $z$, or expression "electrons involved" actually mean?


texts:
My problem is with the methyl group. If it wasn't there, I had no problem.
When the halonium bridge is made does the methyl group shift to give a more stable transition state or not?


texts: Are "gas phase" calculations the same as "vacuum" calculations?

texts: In both molecular mechanics/dynamics calculations and quantum mechanical calculations, the literature often refers to both gas-phase calculations and calculations done in vacuo. Is there actually a difference between these, or are they the same thing? If same, why would we call something a gas-phase calculation if there's no gas there?


texts:
Many molecular biology protocols advice against sterilizing HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) solutions by autoclave.

Supposedly, HEPES is heat labile, and the high temperatures used for sterilization somehow impair the function of the buffer, or perhaps generate unwanted chemical species (this is speculation on my part; I've often seen the advice to not autoclave HEPES, but never seen anything about why not). Typically autoclaves heat solutions to 121C and increase pressure to slightly above 2 atm, which is about a degree short of the boiling point of water. This environment is maintained for 20 minutes in order to destroy biological contaminants.

I have seen this claim often, but had trouble locating an actual source or reasoning for why HEPES should not be autoclaved. Has there been a publication that actually tried to heat a HEPES buffer to autoclave temperatures (121C) and see what happens? What exactly is the consequence, especially with regard to the biological uses of HEPES (ie. pH buffer)?


texts: What makes cola efficient as a rust remover?

texts:
I actually tested submerging a bunch of old rusty knives blades in a cup of plain cola for a few days not expecting much. To my amazement the myth held true, coke is a really good rust remover.

So what is the chemistry behind it?


texts: Why do fluorescence intensities decline with replicate number?

texts:
I am performing a determination of riboflavin with fluorescence spectrophotometry. I've dissolved my riboflavin in a dilute GAA solution, created a calibration curve and measured my unknown's fluorescence.

For these types of analyses I usually perform triplicate measurements, however I've noticed that spectrofluorometric measurements always decrease with replicate number. I assume this is due to 'photobleaching' of my samples. Since the phenomenon occurs with replicate rather than over time, and since my sample is in a dark environment, I would imagine this can only be the result of the excitation light emitted by the instrument itself. I find it surprising that this causes such a dramatic change in fluorescence from measurement to measurement. I also notice that with enough replicate measurements, eventually the intensity decline seems to bottom out. Can anyone explain the specifics of this phenomenon to me?

Am I right in assuming that this is photobleaching (deactivation of the chromophore) rather than photodegredation (breaking the molecule), or are these the same?
How exactly is the fluorophore deactivated?
Can the degree of fluorescence intensity decline be predicted quantitatively?
Would my calibration be more accurate if I used single measurements instead of taking the mean of three replicates?


texts: Why does increasing the available surface area of a pure solid not effect equilibrium?

texts:
Take a reverseable reaction of a gas and a solid, $$\ce{A(g) + B(s) <=> C(g)}$$

The rate of the forward reaction will depend on the surface area of the solid available. If I take that system at equilibrium and add more of the solid, especially if it's in a form with a large surface area this should change the rate of the forward reaction, but this doesn't change the equilibrium. The closest to an answer I've found is that the rate of the reverse reaction increases by an equal amount so that $K$ remains constant, but no justification for that is given.

Increasing the rate of the forward reaction increases the concentration of $C$, which should increase the rate of the reverse reaction, that makes intuitive sense. But I can't see any obvious reason why that should be equal. Presumably my textbook is being a bit reductionist here.

Is it making a simplifying assumption and not bothering to mention that assumption? (the reactions are being considered as independent of surface area? There are unconsidered phenomenon involved where the activity of a pure solid can't be treated as unity and we're only dealing with an approximation?).

Or are there more complex factors at play that result in the rate of the reverse reaction increasing by the same factor as the rate of forward reaction, and the book just doesn't bother to discuss them?


texts: About the equilibrium of a flowing reaction

texts:
Imagine to have a tube (to make a reactor simple) inside which a chemical reactions take place and reactants are constantly fed so overall can be considered in steady-state conditions.

Just to pick one, I assume the reaction to be exothermic.

Now in my mind there are the following two options, one of them is not clear.

Assuming that the tube is cooled and kept to a constant temperature and that the reaction is not controlled by kinetics, I think that at the end of the tube (if long enough) it can be considered in thermodynamic equilibrium.
If the tube is adiabatic then a distribution of temperature inside should arise. For each temperature there exists an equilibrium constant, and thus a different composition. In this case, would there be thermodynamic equilibrium at each single step (infinitesimal) along the tube? Again, this is considering an equilibrium-controlled reaction.


texts: How are these compounds strong bases, when they are sparingly soluble in water?

texts:
How is it possible that some insoluble compounds in water, e.g. $\ce{Mg(OH)2}$, $\ce{Ca(OH)2}$, $\ce{Sr(OH)2}$ are considered strong bases?

Are they even strong bases? How can I tell if a compound is a strong base or not?

Is it possible to explain with equations and/or formulas what happens when these compounds are dissolved into water?


texts:
What is the difference between melting and dissolving? I am looking some general features.

The answer should be adaptable to the melting/dissolving of ice cube (water) in a class of pure alcohol (ethanol) just below (or at the) melting point of ice, or similar phenomena.

I am now assuming that the ice is dissolving and melting at the same time.

In other words which reaction energy is higher in the following reactions:

$$\begin{align}
\ce{H_2O(s) &\to H_2O(l)\\
H_2O(s) + n EtOH(l) &\to H_2O \centerdot (EtOH)_{n}}
\end{align}$$

Or, are there substances that release more energy in dissolvation than consume in melting?


texts: Why the second and third ionisation enthalpy of Bismuth is more than that of Antimony?

texts: The  first ionisation enthalpy values of Group 15 elements follows a descreasing trend due to increasing atomic size and metallic character but why the second and third ionisation enthalpy values follows such a anomalous trend ?


texts: Can PDMS silicone be produced with dichloromethane?

texts:
I was taking a simulated admission test for a Technology Institute (Brazilian ITA) and one of the questions asked for the production of PDMS silicone via these described steps:

Reaction of $\ce{SiO2}$ with carbon, freeing $\ce{CO2}.$
Non-volatile product of (1) reacting with dichloromethane in a $\ce{H2}$-rich atmosphere.
Product of (2) reacting with water giving PDMS and $\ce{HCl}.$

The proposed solution was:

$$
\require{enclose}
\begin{align}
\ce{SiO2 + C &-> Si + CO2}\tag{1}\\
\ce{Si + 2 CH2Cl2 + 2 H2 &-> Si(CH3)2Cl2 + 2HCl}\tag{2}\\
\ce{n Si(CH3)2Cl2 + n H2O &-> \enclose{horizontalstrike}{\;(}OSi(CH3)2\enclose{horizontalstrike}{)_n} + 2n HCl}\tag{3}
\end{align}
$$

However, this route does not follow the Rochow process (direct process) with chloromethane on step number 2. This created confusion among the students who took the test because it was hard to know if this route even existed and that $\ce{HCl}$ had to be dispensed on step number 2 to balance the equation.(Weird to come up with this by yourself.)

The question that remained among the confusion is:

Can PDMS be produced via this dichloromethane route?

Haven't found any information directly related to this on the internet.


texts: How can we determine the Acidity or Base only from information molecular formula provides?No concentration given

texts: How can we determine the Acidity or the base of a solution just from the information the molecular formula provides, like $\ce{KCl}$, $\ce{NH4Cl}$, $\ce{MgSO4}$, $\ce{NaCO3}$, like which ones have a pH of less or more than 7, if I was given the concentration , I would have used $-\log{\ce{[H3O+]}}$ formula, but without it, how can I determine the pH levels?


texts:
In methyl isocyanate, $\ce{CH3CNO}$, shown below,

 it seems that the nitrogen lone pair can resonate with the carbon oxygen double bond, generating a resonance structure something like acetonitrile oxide:

In that case, why is the geometry around the nitrogen in the methyl isocyanate compound bent and not linear? Can the lone pair even resonate like that?

I remember in Klein's organic chemistry, it is stated that

  Whenever an atom possesses both a π bond and a lone pair, they will not both participate in resonance

In methyl isocyanate, $\ce{CH3CNO}$, shown above, it seems that the nitrogen atom has both a π bond and a lone pair. So perhaps the sp2 lone pair on nitrogen atom cannot resonate with the carbon oxygen double bond? I am not sure.


texts: What is the "coefficient of ionization" or "ionization coefficient"?

texts:
The question got bumped and I looked at it. The OP seems to use the two terms coefficient of ionization and ionization coefficient interchangeably and assigns the variable $\alpha$. The problem is in part asking about the pH of a 0.1 molar ammonia solution.

Am I correct to assume that the ionization coefficient is the fraction of the ammonia that has ionized?

My google foo is off today. I couldn't find a formula anywhere where the context made sense. The problem in question has nothing to do with a plasma.


texts: Can 32% hydrochloric acid be stored in a milk jug (HDPE)?

texts:
Can $32\%$ ($20$-degree Baume) hydrochloric acid (typically found as 'muriatic acid' in hardware stores) be stored in a milk jug?

I have read that acids can be safely stored in polyethylene bottles. The milk jug I have has the HDPE resin ID code on it. However looking at Wikipedia, it is clear that HDPE is used to make a wide range of products with different "strengths". Given the "squishiness" of milk jugs, I would assume it is on the lower end of the "strength" scale. Does this make it any less suitable for holding diluted hydrochloric acid?

Context: I plan on etching some circuit boards as per this tutorial. And I am looking for places to store the resulting copper (II) chloride solution.

$$
\ce{Cu + 2HCl + H2O2 -> CuCl_2 + 2H2O}
$$

I am assuming that if the container can hold hydrochloric acid, it can hold the resulting copper(II) chloride solution.


texts: Periodic trend in difference of energy between the s and p orbitals

texts:
Why does the difference of energy between the 2s and 2p orbitals of the second period elements increase with increasing atomic number? Does this difference increases by moving down a group, e.g. is the difference between 3s and 3p bigger than 2p and 2p and why?

  Atomic Orbital Ionization Energies, eV
  $$
\begin{array}{lccccc}
\hline
\text{Atom} & \mathrm{1s} & \mathrm{2s} & \mathrm{2p} & \mathrm{3s} & \mathrm{3p} \\
\hline
\ce{H} & 13.6 & & & & \\
\ce{He} & 24.5 & & & & \\
\ce{Li} & & 5.45 & & & \\
\ce{Be} & & 9.30 & & & \\
\ce{B} & & 14.0 & 8.30 & & \\
\ce{C} & & 19.5 & 10.7 & & \\
\ce{N} & & 25.5 & 13.1 & & \\
\ce{O} & & 32.3 & 15.9 & & \\
\ce{F} & & 46.4 & 18.7 & & \\
\ce{Ne} & & 48.5 & 21.5 & & \\
\ce{Na} & & & & 5.21 & \\
\ce{Mg} & & & & 7.68 & \\
\ce{Al} & & & & 11.3 & 5.95 \\
\ce{Si} & & & & 15.0 & 7.81 \\
\ce{P} & & & & 18.7 & 10.2 \\
\ce{S} & & & & 20.7 & 11.7 \\
\ce{Cl} & & & & 25.3 & 13.8 \\
\ce{Ar} & & & & 29.2 & 15.9 \\
\hline
\end{array}
$$

Data source: www.colby.edu


texts: Is it possible to use glycerol DNA/RNA drying during extraction?

texts: Is it possible to use glycerol with ethanol in order to avoid over-drying of DNA/RNA at drying step of extraction protocol?


texts:
This is a follow up on "Generally Octahedral - Meaning?".

Since Dissenter asked in the comments to my answer:

  I'm not sure why the $\ce{F_{eq}-S-F'_{eq}}$ bond angles would be compressed, even if the $\ce{S}$ were out of the plane.

Since ron's answer already satisfies the original question about $\ce{BrSF5}$ and I did not want to clutter my answer even further, I am asking it here in a Q&A style.

How does the pyramidalization effect the bonding angles in a distorted octahedral environment?


texts: What's a minimal yet chemically-meaningful kinetic system for an oscillating reaction?

texts:
Oscillating reactions are a funny aspect of chemistry. I have tried to find various simplified kinetic models of oscillating reactions such as the Belouzov-Zhabotinsky, the Briggs–Rauscher or the Bray–Liebhafsky reactions in order to be able to study them. However, the models I have found so far are either too complicated (8 or more species considered), or loose chemical significance. For an example of the second case, Ball's 1994 model[1] corresponds to:

While this is useful and introduces a nice circularity in the model, creating the possible feedback, it has lost all chemical sense — by which I mean that no correspondance can be established between the species of this model and a real oscillating system.

So, my question is: what's the simplest known chemically-meaningful model of an oscillating reaction?

[1] Ball, P. 1994 Designing the molecular world: Chemistry at the frontier. Princeton, NJ: Princeton University Press.


texts: What happens when a semipermeable membrane allows only one solute to pass through?

texts:
I'm essentially a medical student where we deal a lot with osmosis. But when we are taught, it is done generally with only a single solute in consideration.

What if two different solutes are used on either side? The membrane being permeable only to one, not the other but also free for water to move.

Lets assume a beaker of base 10cm x 20cm, of any height. Add 2 litres of water to it, it would come to a height of 10cm. Dividing the beaker equally into two with the semipermeable membrane of the specifications, we'll be left with 1 litre on each side. Now add 1 osmole glucose on one side and 1 osmole NaCl on the other (you can't add only Na+ ions). Where glucose and water can move but NaCl wont.

I guess it'll be safe to assume that $\ x$ moles of glucose moves to the other side resulting in a change in concentration on both sides. Now the water would also move causing not only a change in concentration due to the change in volume distribution but also a change in hydrostatic pressure.
Let the change in height be $\ y $ cm. Now the only constraint I can think of is that the pressure on either side should be equal at the base. By pressure i mean the sum of both hydrostatic and oncotic pressure. Oncotic pressure is given by $\ P_o = icRT$ and hydrostatic is by $\ P_h = h\rho g$.

Now I write $$\ P_{o1} + P_{h1} = P_{o2} + P_{h2} $$

That'd give $$\ (h+y)\rho g + \frac{n+x}{(h+y)A}RT = (h-y)\rho g + \frac{n-x}{(h-y)A}RT$$

Where $\ h$ is the height 10cm , $\ n$ is the no. of moles which we fixed as 1 mole (or rather, osmole) So rest all are constants and the only variables left here is $\ y $ and  $\ x $ which we need.
So rest all are constants and the only variables left here is $\ y $ and  $\ x $ which we need.
 On solving, the equation comes to a cubic in $\ y$ which is actually not so desirable!! Also we need another equation, since it is an equation with two unknowns. So I showed all this since this is the way I would proceed. But I am now stuck.

P.S This was a post on the biology forum and then the physics forum too, a discussion of which I extended here.


texts: Why doesn't aromatic substitution add at multiple positions in one reaction?

texts: When you do aromatic substitutions, you usually see the major products with one substituent added. My question is why can't you add multiple substituents in one reaction? For example, the image below shows nitrobenzene reacting with $\ce{Br2}$ and $\ce{FeBr3}$ to add $\ce{Br}$ to the meta position. Why can't the reaction continue and add to the other meta position and thus make 1,3-Dibromo-5-nitrobenzene?


texts: What is the product obtained when methyl vinyl ketone is reacted with 1,2-ethanedithiol and the product is further hydrogenated with Raney Nickel?

texts:
I was solving questions from aldehyde, ketones and ethers and I came across a question that asks:

What is the product obtained when Methyl vinyl ketone is reacted with 1,2-Ethanedithiol and the product is further hydrogenated with Raney Nickel?

My thoughts:

I thought that the reaction could be similar to the one where we react a ketone with ethylene glycol, then on further hydrogenation the double bond breaks. I may be wrong. Any help will be highly appreciated


texts: Is there a name for this algorithm to calculate the concentration of a mixture of two solutions containing the same solute?

texts:
There is an algorithm called "Mischungskreuz" (German for "x of mixing") that is sometimes taught as a shortcut to figure out the following problem:
You have two solutions that contain a solute at different concentrations $c_1$ and $c_2$. At what ratio $V_1/V_2$ do you have to mix them so that the mixture has the desired concentration $c_m$?
For example, let's say you want to make a 22% solution from a 35% and a 15% solution. You write the desired concentration in the center and the available concentrations at the left ends of the "x", and get the ratio of volumes on the right side of the "x" as shown below:

So in this case, mix 7 parts of 35% with 13 parts of 15% solution to get the desired 22%.
Source: https://de.wikipedia.org/wiki/Mischungskreuz
My questions are: Is this method taught outside of Germany, and is there a non-German (maybe English?) name for it?


texts: I'll be doing some work (as a software engineer) with a vacuum process chamber that consumes various nasty gases.  There are numerous safeguards in the system, but as a cautious type, I decided to read the MSDS of the chemicals involved.  The one that makes me the most nervous is tungsten hexafluoride; one mole apparently reacts with water to form 6 moles of HF, which I distantly remember from chemistry class as being bad news.  Being largely composed of water, I find this troubling.  If there were failures in the multiple safeguards and a leak did somehow occur, how could it be detected?


texts: Finding a stable conjugate base when comparing nitrogen vs. a triple bond

texts:
I am trying to understand acid-base reactions and I am trying to figure out which conjugate base is more stable.

The molecule on the top with dashed lines around the $\ce{H}$ is the original molecule and then below it I remove $\ce{H}$ and see what the resultant conjugate base looks like. I don't understand why the bottom left conjugate base is less stable than the one on the right.  Why doesn't nitrogen create a more stable conjugate base than the triple bond?


texts: How does different diffraction grating effect resolution and sharpness of lines in a line spectrum?

texts:
In my lab notebook it asks us to think about the spectroscope further than the reading goes on.

It asks if we use a diffraction grating that contains 600 lines/mm in the spectroscope what do we expect would happen to the lines of the line spectrum in terms of sharpness and resolution.

Is the answer (assuming 600 is more than normal) that the lines would be both more sharper and have a higher resolution? My first thought was that the lines would be skinnier but more clear.


texts: Is there a finite number to the possible state of electron in an atom?

texts:
Okay, I know you may say, there are infinite numbers of possible state of an electron between its ground state and ionic state, since energy levels get continuous as electron gets farther away from the nuclear. But that's not what I mean.

Here is my concern: Any linear combination of eigenstates is also a state for an electron in an atom. For example, an electron in 3d orbital (n=3, l=2) is thought to have only five possible states: dxy, dxz, dyz, dx2-y2, dz2, with literally no m eigenvalue. Yet, what about there linear combinations? Aren't they also possible states of an electron in 3d?

Thanks for any help!


texts: How can this ketone show Cannizzaro reaction?

texts: According to answer key, Cannizzaro reaction of 3-hydroxy-2,2-dimethyl-1-phenylpropan-1-one (a ketone) takes place but how is that possible when we know only aldehydes show Cannizzaro reaction?


texts: Water with Sodium VS Alcohols with Sodium

texts:
Why is the reaction between water and sodium more vigorous than that between ethanol and sodium?
Also, why does the reaction between sodium and an alcohol becomes less vigorous the longer the hydrocarbon chain?


texts: What do you mean by "periodic" in the periodic table?

texts:
Modern periodic law states:

  “The physical and chemical properties of the elements are periodic
  functions of their atomic numbers”.

But I don't think this is so! (Forgive me for my stupidity. But please try to understand what I am saying and if you find any mistakes then please let me know).

If I consider the property of Li then I find that after 7 element there comes an element Na which have similar properties like Li. Now according to periodic law I must get another element which has similar properties to that of Li after 14 elements. And indeed I found one named K . Now again the same thing must happen (no?) ie, there must be an element which have similar properties to Li and is 21 elements away(Mn). But I don't find such element! Why?

The properties of Element is periodic so why then this "periodicity" doesn't hold in case of Li?


texts: Wavelengths of colors emitted by alkali metals during flame test

texts: While reading my NCERT chemistry book (Pg no.-300), I came across  a table that mentions colors emitted by alkali metals and corresponding wavelengths.  It mentions that Potassium emits violet color(As far as I know it's more close to lilac) but corresponding wavelength written is 766.5 nm (I mean this is closer to red region) which does not even lie in visible spectrum range...  Does that mean that infrared rays are emitted and book suggests that or is it wrong to say so?


texts: Why there are more examples of carbonylate anions than metal carbonyl cations?

texts: I know that metal carbonyl complexes that do not follow EAN rule or 18 electron rule try to achieve that by gaining electron (forming carbonylate) or loosing electron (forming carbonyl cations). But this question is way too dicey. It came in a national level exam in our country. I am yet to find a solution.


texts:
I was sent data for a molecule referred to as 1,2'-bis(4-aminophenoxy)benzene. I haven't been able to figure out if that is a real molecule.

If I drop the prime, I know 1,2-bis(4-aminophenoxy)benzene should look like that:

and Google agrees. But with the prime, I have no idea what the molecule could be. Is there such a molecule, or is it a typo?


texts: Why does hydrogen burn with a pop sound?

texts:
Our teacher made us to do an experiment with zinc granules and hydrochloric acid.

$$\ce{2HCl + Zn -> ZnCl2 + H2}$$

We collected the hydrogen gas that was evolved in a test tube and on ignition, it burned with a "pop" sound. Why does hydrogen show this behavior? Why doesn't it burn more quietly like other fuels (gasoline, coal, wood, etc.)?


texts:
My teacher told me that electrolysis of dil. $\ce{H2SO4}$ (concentration below $50\%$) using inert electrodes results in gradual increase of the concentration of $\ce{H2SO4}$.

I can't seem to figure out why. I know that the sulfate ions will remain in the solution, but aren't the $\ce{H+}$ ions of $\ce{H2SO4}$ reduced at the cathode as well?

Another doubt I have is that I've seen different equations for the oxidation at the anode for this electrolysis in different books. Some of them show that $\ce{OH-}$ will be reduced, and some show that $\ce{H2O}$ will be reduced! I'm really confused about all this.


texts:
I understand that the strength of HF differs significantly depending on the concentration. I understand the basic theory behind this - homoassociation - and stabilization of the highly negative charge dense fluoride anion through hydrogen "bonds"/intermolecular attractions with undissociated solute $\ce{HF}$ molecules.

However, I am unclear on the Wikipedia explanation of homoassociation:
http://en.wikipedia.org/wiki/Homoassociation

Regarding the equations - I cannot tell if the authors meant to refer to pure, liquid $\ce{HF}$ or a solution of HF. I'm thinking that the authors are referring to liquid $\ce{HF}$ because auto-ionization of HF is mentioned. I'm thinking that auto-ionization would only be significant in liquid $\ce{HF}$. Or in a concentrated solution.

Also, regarding the second equation - the authors make it look like the fluoride anion is forming an actual, intramolecular, bond with the $\ce{HF}$ molecule. I think the authors are implying the formation of an intermolecular hydrogen bond, correct?

On the other hand the bifluoride anion seems to be a real molecular entity (http://en.wikipedia.org/wiki/Bifluoride).

This only muddies the water further. I.e. which of the following best represents how the fluoride anion is stabilized, causing concentrated solutions of $\ce{HF}$ to ionize further than one would expect from $\ce{K_a}$ values?

$\ce{HF}$ ... $\ce{F^-}$ (hydrogen bonding)

or

$\ce{HF_2^-}$ (formation of bifluoride anion)

Also, any further links to resources about homoassociation would be appreciated.

ETA: Also, can't the fluoride anion form hydrogen bonds with water? The fact that concentrated HF is stronger than dilute HF than what mere $\ce{Ka}$ values suggest implies that H-bonding with water isn't as effective as H-bonding with HF molecules. Why? Is water less polar? On the other hand water can form a maximum of two hydrogen bonds with the fluoride anion, while a HF molecule can only form a maximum of one hydrogen bond with a fluoride anion.


texts: Mechanisms of Birch and Bouveault-Blanc Reductions

texts:
The question is all about the sequence of a possible Birch- and Bouvault-Blanc-Reduction in this exemplary substrate. With which reduction the mechanism begin?

My first attempt was to classify the aromatic system as a nucleophilic center, whereas the ester group as an electrophilic center. But as which should the solvated, "free" electron be classified? Maybe, because of its charge, simple as a nucleophilic reagent, which therefore first attacks the nucleophilic aromatic ring? Is this simple explanation right? Because in the Bouvault-Blanc reduction the attack also takes places on the nucleophile, partial negatively charged O-Atom.

This question was inspired by the II,5th Supplementary problem of the book "The Art of Problem solving in Organic Chemistry" (Alonso-Amelot, Second edition). There, the Birch reduction takes place first, but the author delivers (for me) no neat explanation.


texts: Could chromatography induce a conformational change?

texts:
We'd been studying chromatography in our instrumental analysis course and I was wondering if chromatography could induce a conformational change.

For example, you have a straight chain with a hydrophobic side and hydrophilic side; when relaxed, its conformation is such that it has a hydrophilic outer surface and a hydrophobic core.

If you run it through a normal phase column, could the stationary phase cause a change in conformation to, let's say, a hydrophilic core and hydrophobic outer surface?

Also, if this could happen, then it would initially go through the column at a rate similar to the mobile phase and then slow way down, yes? If so, what would be the implication? Would the peaks be broadened?


texts: Can I pour a solution into another vessel with no air bubbles?

texts:
I have been trying to create a method to create a homogeneous agar solution.

What are appropriate techniques to ensure homogeneous solidification of an agar-based aqueous solution?

The new solution consists of distilled boiling water, $\pu{20 g/L}$ agar, $\pu{10 g/L}$ $\ce{NaCl}$ and $\pu{1 g/L}$ $\ce{CuSO4}$.
An issue with the agar is that it only dissolves between 90-100C which makes it difficult to dissolve using a hot plate or other methods as it also needs to be homogeneous.

I've made progress speaking to both the microbiology and chemistry departments of my university. The current idea to make the solution homogeneous is to heat it in an autoclave set at 121C. This will also sterilize the solution making the phantom last longer. Unfortunately we have no 3L beakers to do it all in one go. They have plenty of 2L and some 5L beakers, but nothing that is 3L.

A new idea is to heat a round bottomed flask in the autoclave and then transfer the semi-cooled solution to a perspex container that will have a base on it. (flask and container shown in the photo below)

The problem is how do we ensure the solution is still relatively homogeneous and won't be full of air bubbles? Are there any simple ways to solve this?


texts: Why can we disregard stoichiometric coefficients when computing reduction potentials?

texts:
A $\ce{Cr(s) | Cr^3+ || Cd^2+ | Cd(s)}$ galvanic cell has redox half reactions:
$$
\begin{align}
\ce{Cd^2+ + 2e- &-> Cd(s)} &\quad E^\circ &= \pu{-0.4 V}\tag{R1}\\
\ce{Cr^3+ + 3e- &-> Cr(s)} &\quad E^\circ &= \pu{-0.7 V}\tag{R2}
\end{align}
$$
Balanced reaction equation then is
$$\ce{3 Cd^2+ + 2 Cr(s) -> 2 Cr^3+ + 3 Cd(s)}\tag{R3}$$
$$E_\mathrm{cell} = E_\mathrm{red} + E_\mathrm{ox} = \pu{-0.4 V} + \pu{0.7 V} = \pu{0.3 V}$$
Why is $E_\mathrm{cell}^\circ$ independent of molar coefficients $(3,2)?$


texts: Should carbon tetrachloride really be considered an organic compound?

texts:
Wikipedia says:

  Carbon tetrachloride […]  is an organic compound with the chemical formula  $\ce{CCl4}$.

From an organic point of view, carbon tetrachloride can be called the tetrachloro derivative of methane and is described in many organic textbook along with $\ce{CH3Cl}$, $\ce{CH2Cl2}$ and $\ce{CHCl3}$.

From an inorganic point of view, carbon tetrachloride can be considered chloride of a group 14 element (along with $\ce{SiCl4}$, $\ce{GeCl4}$).

Shouldn’t carbon tetrachloride be considered an inorganic compound? It neither contains any $\ce{C-H}$ bond nor is it found in any living organism.

Tetrachloromethane is its organic name. But it is generally not called by this name. Carbon tetrachloride is its better name and inorganic compounds are named like that.


texts: Why is chromate stable in basic medium and dichromate stable in acidic medium?

texts:
When I was studying the equilibrium existing between chromate and dichromate ions in the solution, I came to know that

  Chromate ion is more stable in basic medium while dichromate ion is stable in acidic medium.

However, I am not able to understand what is the governing factor to decide which species will exist to a greater extent and how the equilibrium shifts the direction on changing the nature of the medium.

Why is chromate stable under basic conditions and dichromate stable under acidic conditions?


texts: Will heating diatomic oxygen enough break the O=O bonds?

texts: The bond enthalpy associated with a $\ce{O=O}$ double bond is equal to 495 kJ/mol. Does that mean that adding enough kinetic energy in the form of heat will eventually cause the bonds to break and create monoatomic oxygen?


texts: Is there an exothermic reaction which produces 1 to 2 minutes of heat at around 175 degrees Fahrenheit, no toxic gasses and is considered to be more or less safe?


texts: When an iodide/iodate solution is acidified with H2SO4 instead of thiosulfate, why should it be titrated immediately?

texts:
My class is currently performing a reaction to determine the oxidizing power (i.e. the amount of hypochlorite) of household bleach. The general process is as follows:

Standardize thiosulfate to be used as a titrant of $\ce{I2}$ solution.

An excess of I- ions are allowed to react with a known amount of $\ce{KIO3}$ in acidic solution.
The iodine formed from this reaction is titrated with thiosulfate using starch as an indicator of triiodide anion.
The relation between moles $\ce{KIO3}$ and thiosulfate is used to determine molarity of thiosulfate.

Analysis of oxidizing capacity of liquid bleach

Excess iodide ion solution added to bleach.
Iodide ions are oxidized to I2 after this solution is acidified simultaneously with the reduction of hypochlorite.
The iodine that is formed is then titrated with the above standardized thiosulfate solution.
The indicator (starch) is not added until the dark-brownish color of the iodine has changed to pale yellow. When it is added, the solution color changes to blue black.
The end point of titration is indicated when the solution becomes colorless.
(Note that if the starch is added too soon in the titration, the formation of the blue-black complex is not easily reversed, making the end point very slow and difficult to detect.

Pertinent reactions are given below

Reactions Pertaining to Titration

$\ce{HOCl + 2I- + H+ -> I2 + Cl- + H2O}$

$\ce{2S2O3^--  + I2 -> 2I- + S4O6^--}$

$\ce{HOCl + 2S2O3^-- + H+ -> Cl- + S4O6^-- + H2O}$ [the addition of the above two reactions]

$\ce{I3- + starch <-> starch*I3-(complex)}$  [blue-black in solution]

Reactions pertaining to the standardization of thiosulfate

$\ce{IO3- + 5I- +6H+ -> 3I2 + 3H2O}$

$\ce{3I2 + S2O3^-- -> 6I- + 3S4O6^--}$

The question

We were told that, during the standardization process, if the iodate-iodide solution is acidified with $\ce{H2SO4}$, it should be titrated immediately. My question is why? Using thiosulfate, this is not the case, correct? Why does this change when sulfuric acid is used in its stead?


texts: Does the probability function for a molecule to have energy in a certain mode depend on the minimum required quantum energy level of that mode?

texts:
I understand that the probability density for a particular velocity v+dv in one dimension for a molecule in a system is:
$$f(v) = \sqrt{\frac{m}{2\pi k_B T}} \cdot e^{\frac{-mv^2}{2k_B T}}$$
I'm noticing that this formula does not distinguish the type of freedom in which the concerning velocity is used. So basically this formula would say that a certain velocity in a translational degree of freedom has an equal probability as the same velocity in a rotational or vibrational degree of freedom, which is incorrect from what I know due to the different required minimum quantum energy for each type of mode (depending on the molecular structure) with respect to the energy that the molecule possesses.
Is there a formula that takes the type of mode into account for the probability?

I found a source that takes the frequency of a degree of freedom into account and calculates its minimum required energy according to hf = E but I don't know how to incorporate that formula into the probability function.


texts:
so according to my understanding orbitals can hold s can hold 2 electrons and p can hold 8 electron d hold 18 and f can hold 32. wouldn't this violate the octet rule? which say only the first shell can hold 2 electrons and the rest of the shells 8. im also confused why some websites says that each orbital has 2 electrons, s has 1 orbital  (2 electrons) p has 3 orbitals (6 electrons) d has 5 (10 electrons) and f has 7 orbits ( 14 electrons)

im so confused guys plz help me as simple as possible


texts:
One of the questions in a recent past paper I completed was:

  One way to make water from the reservoir suitable for drinking is by distillation.

  Describe how water is distilled.

And I answered (perhaps too succinctly) that "The water is vaporised and the condensation is collected."

I would have thought my answer correct, in that it fully addresses the question, however, the mark scheme mentions two points I did not make:

I should have mentioned heat.
I should have mentioned cool (the mark scheme's words, not mine).

But I was wondering, are these two (common) aspects of distillation actually necessary to distill water?

Surely heating and cooling are not really necessary to distill water; couldn't pressure be reduced to evaporate the water, and increased again to condense it?

Or, in the context of the question, is the heating perhaps necessary to sterilise the water (for killing microbes)?


texts: Could a lead-acid battery electrolyte be replaced by hydrochloric or nitric acid?

texts: Hydrochloric acid, as well as nitric acid, are also strong acids like sulfuric acid. So, why are not they used commercially in lead-acid batteries?


texts: At what pressure will hydrogen start to liquefy at room temperature?

texts: I want to increase a fixed-size object's internal gas pressure by generating hydrogen in it, but I could not find the proper phase diagram for it. So I am wondering how high pressures I can get.


texts: Change in internal energy for the heating and vaporisation of water

texts:
What is the value of change in internal energy at $\pu{1atm}$ in the process $$\ce{H2O(l,$323\ \mathrm K$)->H2O(g,$423\ \mathrm K$)}$$
  given $C_{\mathrm m,V}(\ce{H2O,l})=\pu{75.0 J K^{-1} mol^{-1}}$ and $C_{\mathrm m,p}(\ce{H2O,g})=\pu{33.314 J K^{-1} mol^{-1}}$

  a. $\pu{42.91 kJ/mol}$
  b. $\pu{43086 kJ/mol}$
  c. $\pu{42.6 kJ/mol}$
  d. $\pu{49.6 kJ/mol}$

I tried to use the First Law here. For chemical reaction I found $\Delta n_\mathrm g$ to be $1$ and the heat of the reaction $\Delta H$ is given as $\pu{40.7 kJ mol-1}$. However, I am not able to use the specific heat data given in the question. What am I doing wrong here?

I am getting stuck in phase change reactions, particularly in using $C_p$ and $C_V$ here. I know the First Law will work, but how do we use $C_p$ and $C_V$ in such reactions?


texts: My confusion regarding Hydrogen peroxide

texts:
In Hydrogen peroxide, the oxidation number of oxygen is "-1" instead of "-2".

But it seems to me that, the oxygen atoms have '-2' as their oxidation number as each oxygen atom here is connected to a hydrogen atom and an oxygen atom.

So, what's actually happening here?

If there's any problem in my question please inform me. Thanks!


texts:
Many articles say

even numbers of layers or bulk crystal MoS2 have D6h point group
and odd numbers of layers (including monolayer) MoS2 have D3h point group

But whenever looking at the figure of MoS2, I can't recognize there is a symmetry representing the number '6' which means 6-fold(?). With the point group flow chart,

The final answer is C3h for the bulk MoS2.

If I included the inverse symmetry with C6 symmetry, then it would give D6h? Is the inversion symmetry necessary, then why? Especially, if you can point out the six ford axis in bulk case or two layers MoS2, please let us know.

I got the hind from the reference document that Mo has D3h and S has C3v. And these two are factor group of D6h. But I don't much know about group theory... So definitely it is not D6h?

Here the unit cell of bulk 2H-MoS2

Here the top and side view of 1H-MoS2


texts: How to maximize shelf-life of freeze-dried food beyond 25 years? Can this exceed 100 years?

texts:
Many manufacturers will sell and advertise emergency preparedness food packs to still taste "great" 25-30 years into the future (or at least maintain a consistent taste over this period). For instance, they will cook eggs, lasagna or vegetables (anything really), then place it into a freeze-drier unit, which eliminates the water via sublimation. They then place the food product into a mylar or aluminium pouch (sometimes polyurethane), insert an oxygen dissector pouch in it, then instruct the customer to store it in a cool (less than 16 degrees Celsius or 60 Fahrenheit) and dry environment for long term storage.
What process happens after 25-30 years which limits its shelf life? It is the accumulation of oxygen diffusing within the bag over time? It is the oxygen pouch that reaches it absorption limit? Is moisture sneaking in? Is the organic structure of the food break down due to normal thermodynamic forces over time (increase in entropy)?
What if one wanted to increase the shelf-life to say 50 years, maybe even 100 years. What food break down processes will be encountered as the limiting factor, that would need to be countered?
What other tricks (other than mylar pouch, oxygen desiccator pouch, freeze-drier) can I use to maximize the shelf-life in excess of 100 years?


texts: Increasing elasticity of microcrystalline wax

texts:
I'm doing sculpture and I've been playing around with some microcrystalline wax. The pliability of it once warm is great, but I'm running into the problem of it tearing / ripping when I stretch it. The same issue causes problems when smoothing it out, as the surface "gives way" under my finger if I press hard enough.

I've tried mixing in petrolatum and mineral oil in various different quantities but with no success; both just make the wax stickier and softer with no elasticity benefits. Is there another method which will increase the stretchiness?


texts: Aside from carbon, what other substances can be made "superhard"?

texts: So diamonds are an allotrope of carbon, that is formed when carbon is put under immense pressure, right? What other elements or compounds can you make into "diamonds", as in more durable, harder versions of themselves? What happens if salt or iron for example, is put under immense pressure, do they become harder too?


texts: How should you name the solid-solution compound ScY(SeO4)3?

texts: How should you name the compound $\ce{ScY(SeO4)3}$? There are 2 cations, and I know that $\ce{SeO4}$ is a polyatomic ion with $-2$ charge. However, I am unsure how to proceed.


texts: Naming convention for buffer solutions/systems

texts:
Is there an official naming convention to follow for buffer solutions/systems? I've noticed that the name of the buffer usually just follows the name of the salt (ex. sodium acetate buffer), but what if the buffer is diprotic?

If I mixed tartaric acid with its double salt, potassium sodium tartrate, would the resulting buffer simply be "potassium sodium tartrate buffer"? Or would it be something like "bitartrate-tartrate buffer"?


texts: Energy of eclipsed and staggered conformations of ethane and propane

texts:
Which points on the given energy diagram represents eclipsed confirmation of ethane and staggered confirmation of propane respectively?

Attempt: Eclipsed configuration is unstable because of repulsions between filled $\sigma$ or bonding orbital and the anti or staggered configuration is more stable due to interactions between filled $\sigma$ orbital and empty $\sigma^*$ orbital.
From the given diagram, either R or S could represent eclipsed confirmation of ethane and P or Q could represent staggered confirmation of propane.
Since they are different compounds, they should lie on different energy diagrams. So the answer could be (R,Q) or (S,P). Which one is correct?


texts: Can equilibrium be reached in a non-reversible chemical reaction?

texts:
Can chemical equilibrium only be achieved in a reversible process?

I have only seen equilibrium in processes that are reversible so I was wondering if it were possible in reactions that are not reversible.


texts: Nucleophilic attack at a carbonyl - angle of attack

texts: What is the specific angle between the carbonyl carbon and the nucleophile during the nucleophilic addition reaction?


texts: Coordination number of carbon in methyllithium tetramer

texts:
According to J. D. Lee's Concise Inorganic Chemistry, the coordination number of carbon in $\ce{Li4(CH3)4}$ is $7$. But the structure of the tetramer is

Doesn't carbon have coordination number $6$ here? Am I missing something?


texts: Steric inhibition of resonance in substituted benzoic acid

texts:
Why does attaching an $\ce{-NO2}$ group at the ortho position of benzoic acid cause $\ce{-COOH}$ to become perpendicular to the plane of the benzene ring? Why doesn't the nitro group get pushed out while $\ce{-COOH}$ stays on the plane?

Also, in the case of two $\ce{-NO2}$ groups attached on the ortho  and meta positions of benzoic acid, both the nitro groups become perpendicular to the benzene ring while $\ce{-COOH}$ remains at an angle to the plane. Why doesn't it become perpendicular this time?

Here is what I referred to for the structure of 2-nitrobenzoic acid :https://pubchem.ncbi.nlm.nih.gov/compound/2-Nitrobenzoic-acid#section=3D-Conformer&fullscreen=true

Here is what I referred to for the structure of 2,3-dinitrobenzoic acid :https://pubchem.ncbi.nlm.nih.gov/compound/2,3-diNitrobenzoic-acid#section=3D-Conformer&fullscreen=true

If you feel these structures arent correct please do give a reference to where I can find the right structure. :)


texts: What is it in the composition of natural fabrics that cause them to retain smoke odors versus synthetics?

texts: Just an observation I notice when around smoker friends or when I visit Las Vegas - polyester clothing doesn't seem to stay smelling of smoke for the rest of the day like my cotton shirts do (or also my hair for that matter).


texts: How can I derive whether the methyl cation or anion is planar?

texts:
According to VSEPR theory, in which species do all the
  atoms lie in the same plane?

  $\ce{CH3+}$
  $\ce{CH3-}$

  (A) 1 only (B) 2 only (C) both 1 and 2 (D) neither 1 nor 2

My try:
Because $\ce{CH3}$ in both forms only are bonded with three hydrogens, they both have one lone pair, which contributes to their tetrahedral structure. So I got D. However, the answer key says that B is the correct answer. How do I get this answer?


texts: Is lithium carbide an ionic compound or covalent?

texts:
I read in my chemistry textbook that lithium carbide (Li4C) is the only carbide amongst alkali metals. As we know, carbides are ionic compounds, and calcium carbide is predominantly ionic (calcium having similar electronegativity value to lithium).
So, is the bond between lithium and carbon ionic? Or is it covalent?

Does a Li4C exist? If so, what is it's nature?


texts: Does iron(III) sulfate react with copper?

texts:
As my understanding, there should be an oxidation-reduction reaction:

$$
    \ce{2 Fe^3+ + Cu → 2Fe^2+ + Cu^2+}
$$

However, I always see the process using $\ce{FeCl3}$ to etch copper, but I never see people using $\ce{Fe2(SO4)3}$ to do this. Is it because such reaction does not occur, or is it because $\ce{FeCl3}$ is acidic in aqueous solution?


texts: Why do you use acetic acid instead of water to create your standard riboflavin solutions?

texts:
I must create my own lab and I was going to use water, however, a similar experiment online says that acetic acid should be used to create my standard riboflavin (vitamin B2) solutions.
Why is that?


texts: For a flat, planar molecule, how do you determine which side is up? Or down?

texts:
I was just reading about alpha and beta linkages in certain cyclic molecules, and it said that the alpha configuration was the one in which a hydrogen was sticking out above the plane, and an OH moiety was below the plane.  A beta linkage for such a molecule had the hydroxyl group upwards, and the lone H below...
But, I cannot find out how you determine which side is 'up' or 'above' and which is 'down' or 'below'...