texts: How does hydraulic equilibrium work on the particulate level?

texts:
I recently learned that osmosis occurs when there is a semipermeable membrane between pure water and a solution of water. The pure water then fills up the solution's side until, as my textbook put it,

"The pressure exerted by this column of solution counterbalances the pressure exerted by the water moving through the membrane from the pure water side."

My question is how does water just naturally want to move from one gradient to the other? Doesn't water move through the membrane both ways? Also, why does water "want" to go to the more concentrated side when the particles move at random?
In other words, why doesn't the flow of water molecules depend on the number of water molecules in the membrane instead of the concentration gradient?


texts: How do I write out the chemical reaction of ammonia with strong acid?

texts:
Write equations for the reactions of each of: (a) nitric acid (b) sulfuric acid *(c) hydroiodic acid, with each of: (i) sodium hydroxide (ii) zinc oxide (iii) ammonia.

So, the reaction of nitric acid with sodium hydroxide and zinc oxide is simple because I know that acid + base = salt + water. Therefore:

$$
\begin{align}
\ce{HNO3(aq) + NaOH (aq) &-> NaNO3 (aq) + H2O (l)}\\
\ce{2HNO3(aq) + ZnO (s) &-> Zn(NO3)2 (aq) + H2O (l)}
\end{align}
$$

It makes sense. In the second part, for example, $\ce{Zn}$ is 2+ and $\ce{H}$ is -1. So using the criss-cross method, you get $\ce{Zn(NO3)2}$ and water. I understand this.

However, with ammonia:

$$\ce{HNO3(aq) + NH3 -> NH4NO3}$$

How am I supposed to know this equation? It's not metal + acid = salt + water. Is there word equations for everything?


texts: Absorption spectrum of common plastic polymers

texts:
I am looking for data regarding absorption spectrum of common used plastic polymers, in the range of 200- 1.000 nm
Moreover, I am looking for inorganic or organic compounds, which can be mixed together with common plastics (PC, ABS, PMMA, POM) and have an absorption peak at 450 nm


texts: Ag-Sn-Cu Phase diagram to formulate homogenization temperature / duration

texts:
I am working on Ag-Sn-Cu alloy phase diagram to figure out the best temperature / duration to homogenize the alloy (annealing). The %age of elements in the alloy are

Ag - 40 %
Cu - 27.8 %
Sn - 32.2 %

(Composition can be varied if necessary but not more than 5 %)

Now the main goal is:

Find out the temperature / time duration at which the ingot of the above said alloy should be annealed to get the maximum Ag3Sn phase in the final ingot. Ag3Sn is the most desired phase with Cu3Sn being the second desired phase. Anyhow the main goal is to make as much Ag3Sn as possible.
The time duration for which the ingot should be placed at the desired temperature. (The total ingot is usually 6–7 kg)
[Supplementary question] Should the temperature be gradually reduced to the desired level of maximum Ag3Sn yield (or gradually increased)?

The phase diagram of Ag-Sn-Cu is as follows:


texts: Why is strontium(II) ion bigger than krypton atom?

texts:
$\ce{Sr^2+}$ is exactly the same as $\ce{Kr}$, in terms of electrons and orbitals.
The only difference between the two, is that $\ce{Sr^2+}$ has a couple of extra protons in the nucleus (and probably a couple of extra neutrons too, but these don't influence ionic/atomic size).
Considering the two extra protons in the nucleus of $\ce{Sr^2+}$, and the overall 2+ charge on the ion,
shouldn't this draw the valence electrons in closer to the nucleus in $\ce{Sr^2+}$ in comparison to $\ce{Kr}$?
(Krypton size= 88 pm, while Sr2+ is 132 pm.)


texts:
can the stability of ortho-hydrogen greater than para-hydrogen can be stated as this?

  The intrinsic energy of ortho is greater than para-hydrogen and also with rise in temperature %of ortho form increase while para decreases and ultimately at room temperature it's 75% ortho and 25% para-hydrogen. Plus as we know that the everything in nature tries to attain lowest possible energy level, and ortho form with opposite spins counteracts each others magnetic moments, making it energetically stable.

Why is it that pure para can be obtained at lower temperature such as 20 K but pure ortho form is difficult to obtain?

I mean when ortho is more stable it should be ortho which should be available more easily than para form?


texts:
Number of planes in $\text{SiH$_2$FCl}$ which contain maximum atoms but all must be different?

I am interested in the above problem. I predicted the answer to $10$ which indeed is $5\choose 3$ because maximum number of points in a plane will be $3$ since the structure is tetrahedral. But the book writes an answer $7$ to the above problem!! Any help will be highly appreciated.


texts: Excitation Source for visible emitting Quantum dots

texts:
I read that the best excitation source for visible emitting quantum dots is UV light of wavelength $\mathrm{360~nm}$ to $\mathrm{380~nm}$. But why should the excitation source have lower frequency than the desired emission maximum?

If the excitation source have lower frequency, the energy of photons in the source will be lower. If that is the case wouldn't it have insufficient energy to excite the electrons from valence to conduction band?


texts: Looking at the IUPAC Blue Book, I noticed that the words “catenane”, “rotaxane” (or “interlocked”, “mechanical bond”, …) do not appear within the rules of nomenclature. Given that a catenane or rotaxane is typically considered a single molecule, I was wondering how these compounds are named. I have read on Wikipedia that catenanes with n bonds are referred to as a [n]-catenanes… but how are specific compounds named?


texts: Why are carbons of Inositol chiral centers?

texts:
I was asked to draw all possible stereoisomers of inositol (1,2,3,4,5,6-cyclohexanehexol). To obtain the answer I had to assume that all six carbons of the molecule are asymmetric, which (bearing in mind possible molecular symmetry) results on the following nine stereoisomers:[1]

The problem is that I fail to see why these carbons can be considered chiral centers. Given:[2]

  The most common cause of chirality in an organic molecule, although not the only one, is the presence of a carbon atom bonded to four different groups [...]. These carbons are now named chiral centers [...]

The chirality of the molecule is not the reason of my doubts, I can see that the only chiral isomers are D- and L- chiro-inositol. Since all carbons in the ring possess a hydroxyl group, can they not be considered to be bonded to equivalent substituents, making them symmetric? Is the possibility of the -OH groups to be above or below the plane of the ring what makes them asymmetric?

From Wikipedia
McMurry, John. Organic Chemistry. CENGAGE Learning, 2008. 7th edition.


texts: Why Atomic size decreases left to right in a period in MPT?

texts: In modern periodic table,  atomic size decreases as we move from left to right in a period. As no. of electron increase left  to right but why atomic size decreases?


texts:
I had an old toner cartridge lying around, so I took it apart and emptied the toner into a jar. I had heard that one could make a ferromagnetic fluid using toner powder and oil, so I mixed a little powder with some kerosene that I had on hand. Turns out, kerosine does something wierd to the polymer part of the toner, and instead of becoming a solution, the toner powder coagulated into a rubbery mass that had a consistency similar to chewing gum.

When I put a powerful magnet from a hard drive next to it, the ball was attracted to it, which surprised me a little, as I had seen on wikipedia that toner had no magnetic components (any more) So, the questio is, Why is printer toner powder magnetic? Is it because carbon is paramagnetic?

Also, what happened to the polymer when kerosine was added?

EDIT

A clarification-
I think the polymer is a resin (based on what the kerosene did to it)


texts: How does the heat capacity of a calorimeter interact with the specific heat capacity of the water inside it?

texts: I saw this basic calorimetry question and it included the heat capacity of the calorimeter (1550 J/°C) but it also included that there were 150 g of water inside the calorimeter as well (4.184 J/(G°C). I saw that in order to calculate the total q, you add q of calorimeter to q of water. I'm having a hard time envisioning why you have to add the two instead of taking only the q of the calorimeter (isn't q of water included in the q of calorimeter?). The question stated that ∆T was equal to +1.211°C.


texts: Why doesn't H₄CO₄ exist as a stable compound?

texts: Why doesn't $\ce{H4CO4}$ exist as a relatively stable compound? Its heavier homologue $\ce{H4SiO4}$ seems to exist although it is unstable to some extent but new methods have been able to stabilise orthosilicic acid using choline chloride.


texts:
I got a question about this molecule, and I'm not sure how to answer it. I know that this one has 4 chiral C-atoms, but I can't seem to get the number of enantiomers right. I know that the formula for the amount of enantiomers is $2^{n-1}$, with $n$ being the amount of chiral centers, which is $4$. So that makes an amount of $8$ enantiomers. But that's not what it says in the answer.

Am I doing something wrong here?


texts: How does aluminium react with bases to form aluminates?

texts:
An example of reaction:

$$\ce{2Al + 2KOH + 6H2O->2 K[Al(OH)4] + 3H2 ^}$$

Aluminium is not ionic, how then does it attract the $\ce{OH-}$ groups to bond with them into the complex ion $\ce{[Al(OH)4]-}$?

I started re-reading non-organic chemistry at a slightly deeper level recently after going through the basics of organic chemistry. This reaction stumped me. I've re-read some stuff about aluminium and complex ions, but can't seem to understand it yet.

There's no positive charge on $\ce{Al}$, yet it reacts with hydroxide groups floating around. Where will the electron from a non-ionic aluminium atom go?

I cannot 'imagine' the reaction, visualize its mechanism, and this makes it hard to remember it.

P.S. Aluminium hydroxide seems to be mysterious in its structure. I quote Chemguide:

  The chemistry textbooks that I have to hand aren't too clear about the structure of aluminium hydroxide as far as the degree of covalent character is concerened, and a web search (until I got totally bored with it!) didn't throw up any reliable chemistry sites which discussed it. Several geology sites describe the mineral gibbsite (a naturally occurring form of aluminium hydroxide) in terms of ions, but whether it actually contains ions or whether this is just a simplification as a convenient way of talking about and drawing a complicated structure, I don't know.


texts: How do I determine which liquids are immiscible with one another?

texts: I am trying to work out which type of ferrofluid I can use to form a weak magnetic seal for a container of liquid photopolymer resin. Is there a mathematical approach to determine what substances will form a solution, and which will remain immiscible, or will I have to buy each ferrofluid and try each one?


texts: Are alkynes more electrophilic than alkenes?

texts:
I think that since alkynes have a greater electron density, they would be less electrophilic than alkenes.

Which functional group is more prone to nucleophilic attacks and why? An example of a known reaction would be greatly appreciated.


texts: Difference in peaks in EDS and XPS spectra

texts:
I have been reading some papers on XPS and EDS and I saw that there's a difference between the width of the peaks (of the same material) in XPS and EDS. Is the reason for this difference because of the better energy resolution of XPS (spectral resolution)? EDS uses the signal from emitted X-rays, whereas XPS uses the emitted electron. There's a limit to what how much energy of the X-rays can be detected (about 2 eV) and electrons are easier in that respect and allow for measurement of lower eV.
Or is there another reason for the difference in the peaks?


texts:
We have products $\ce{A + B}$ combining to form $\ce{C + D}$ through the transition state $\ce{X}$.

Are all reactions at least virtually reversible? Is the difference between a reversible reaction and an irreversible reaction simply that for the former, $\Delta G$ is small, where as the irreversible reaction will have a difference in free energy in products vs. reactants, that the reverse reaction simply doesn't occur, but theoretically could?
Why do concentrations affect the free energy? Is it because you sum the free energy for all reactant molecules, as well as for all the product molecules?

Following is from my textbook:

  [...] the transition state is too unstable to exist for long. It collapses to either substrate or product, but which of the two accumulates is determined only by the energy difference between the substrate and the product -- the $\Delta G$ of the reaction.

I would appreciate if someone could clarify this for me. Feel free to be very nitpicky, I don't want an understanding that is "approximately" correct or "functionally" good.


texts: What does A. R. in A. R. sodium nitrite mean?

texts:
I'm reading about a reaction from a 1970s organic chemistry book. It references A. R. sodium nitrite. What does the A. R. mean?
I see from online that "Ar" means aromatic ring. Is that the same thing?
But I've also seen "Sodium Nitrite, Granular, AR®" with a registered trademark, implying it might be a specific brand of Sodium Nitrite, but that didn't make sense. https://www.chemical.net/sodium-nitrite-acs
Are there different types of sodium nitrite?


texts: Why cant nail polish be used as an acid mask for making a PCB?

texts:
In the question: PCB etching with sodium persulfate, permanent markers seem the most used and experimented with. The thickness of nail polish would give more solid planes and traces.

Might nail polishes resist most common copper etchants mentioned such as:

Sodium Persulphate
Ferric Chloride
Peroxide + Vinegar + Salt

sufficiently for etching a PCB?


texts:
I am given the molecule in black which is treated with $\ce{NaOH}$. The product is in blue.
Could someone explain the mechanism? All I have so far is that the $\ce{-OH}$ group on the bottom right carbon has been deprotonated to $\ce{-O-},$ but am not sure how the rest of the reaction should proceed.


texts: Why is −78 °C a magic temperature for organic reactions?

texts: In many organic reactions that I have seen, running the reaction at $\mathrm{-78\ ^\circ C}$ seems to be quite a popular choice, but I've never seen any explanation for this. What makes this temperature such a popular choice?


texts:
Entropy is maximum at equilibrium, so if we have an equilbrium chemical reaction like:

$$\ce{HI <=> H+ + I-}$$

does it mean that the container of $\ce{HI}$ has maximum entropy or the universe?

Also, constant entropy implies reversibility but I don't understand how  the definition of reversibility applies to a system  of $\ce{HI }$ and $\ce{H+, I-}$ in a container. I mean, there's nothing to actually reverse, is there? By reversibility I mean that the system can be brought to its original state by an infinitesimal change(s) in it's condition.

Could anyone provide an explanation for this?

Note: I have edited my full question because previously it was very unclear.


texts:
Consider a container that contains a mixture of many liquids. Can two of these liquids phase separate without having any significant effect on other liquids inside the container? Is there a feasible scenario where the above can actually happen? I am interested in a scenario where the two liquids only separates themselves from each other and not the rest of the mixture.

More precisely:
Assume the container contains a mixture of liquids A and B with many other liquids (state 1). Can these two liquids separate (triggered by change in the pressure, temperature, ...) so that at the end (state 2) the liquids in the container are divided into two regions with the following properties:

The first region does not contain liquid B. It contains liquid A with the exact same mixture of the other liquid (same as state 1).
The second region does not contain liquid A. It contains liquid B with the same mixture of other liquids (same as state 1).

Indeed we want other liquids in the container to be neutral to the phase separation of the liquids A and B.


texts: Are there many examples of stable, well characterised organometallic compounds of saturated hydrocarbons with beta hydrogens?

texts:
One of the first things you tend to learn in organometallic chemistry is that transition metal compounds containing beta-hydrogens are unstable (there are plenty of stable main groups ones; eg grignards seem pretty stable for most saturated aliphatics). There is a tendency for the beta hydrogen on the alkane to be abstracted by the transition metal leaving a metal hydride and a coordinated alkene, possibly followed by other reactions.

Aryl and alkene ligands are mostly immune to this reaction for various reasons. Similar hydrocarbon ligand with no beta hydrogens are usually much more stable.

But are there any well characterised examples of stable transition metal organometallics with beta hydrogens?


texts:
Is the flip of the cis-isomer wrong? Specifically the image on the bottom right.

What I see is that on the cis-isomer in the first chair, we have an axial upward methyl group and an equatorial upward methyl group. When the ring flips we now have an equatorial upward methyl group (good) and a downward equatorial methyl group (bad). Shouldn't the second one be axial upward? From what I understand, ring flips shouldn't change the orientations of groups; just their axial/equatorial configurations.

Also, in general, would these two rings be equivalent?


texts: What alloys can be used to make a metal pencil like this one?


texts: Calculating the physical properties of isotopes

texts: I am trying to determine the theoretical physical properties (namely melting and boiling temperatures) of isotopic substances.  Harold Urey used Debye thermodynamics (which is quite dense) in his 1946 paper to calculate the physical properties of isotopic substances. Most of the equations appear to be for exchange rates of the isotopes within a given system.  I would like to know which equations are available to determine isotope effects on physical properties of isotopologues and the assumptions that go with them.


texts: Why don't the electrons of opposite spins collide in an orbital?

texts: As I was reading through my textbook, I got to know that in an orbital, there are 2 electrons of opposite spins. My question is: Shouldn't they collide whilst they are rotating?


texts:
From what I understand, the working agent inside a peltier cooler is Bismuth-Telluride. I've read a toxicity data-sheet regarding Bismuth-Telluride here.

If I were to use a peltier cooler inside a sealed cooling system, for example a thermoelectric cooler, will any groceries stored in it be "infused" with Bismuth-Telluride?


texts: pH of aqueous solution of HCl of low concentration

texts:
What is the pH of $10^{-8}~\mathrm{M}$ $\ce{HCl}$ solution in water?

My attempt:

  pH = $-\log(10)^{-8}$ = 8

But this is wrong because it should be acidic. Where have I gone wrong?


texts:
In biochemistry laboratory, it's common for undergraduate students to perform identification of carbohydrates and its functional groups. Bial's test, a method to check if any pentose is present, is one of some ways for the identification. The overall reaction can be found in Wikipedia page (https://en.m.wikipedia.org/wiki/Bial's_test).

The conversion of pentose to furfural has known to me (because I've found the paper) but not the second reaction. I guess some organometallic reactions are involved but not sure to write the mechanism.

I've tried to search the research articles related to the mechanism in Google, Google Scholar, ... or even, Scopus but can't find any paper related to it. This is indeed surprising to me because I thought this classical test should be investigated exhaustively either by spectrometry or computational perspectives.

Any thought or idea is appreciated to present the mechanism (even the mechanism is produced by direct computation).


texts: How pure gold is obtained back from dissolved state in Aqua regia?

texts:
I know Aqua regia is used for purifying gold by dissolving gold in it, but how that dissolved gold is obtained back in the pure state?

I searched everywhere, but I didn't get the answer. So, I am asking here.


texts: In a given sample of water some molecules of water dissociate to give hydronium and hydroxide ion. They say one in 10 million will be dissociated (approx.). What are the reasons behind this? Why water won't dissociate more?


texts: Calculating bond disassociation energy and bond energy for ATP

texts:
I'd like to calculate Bond Dissociation Energy and Bond Energy for ATP to a similar molecule. What free (at least for academic use) computer programs which natively support and document BDE?

If you don't mind, could you provide a tutorial for using those programs to perform the calculations?


texts: What is the justification for Hückel's rule?

texts: I know that experimentally, the rule has been verified but I am having trouble understanding why it works. I see no reason why equivalent cyclic structures can undergo resonance and be just as stable. Any clarification would be nice.


texts: Is it possible to quantify the effects of a chelating agent?

texts: If one wants to see what compound is a more effective chelating agent, how does that get measured?


texts: Why are 4s electrons removed before 3d electrons?

texts:
According to Aufbau's Principle energy of 3d orbital is greater than 4s orbital, so which filling 4s if filled beforehand 3d. Whereas while removing electrons 4s electrons are removed first. Why?

I somewhere read that Aufbau's Principle is true only for ground state. When both 3d and 4s orbital get populated due to some interaction 3d shell is raised a to higher energy level than 4s. It it the case or it has some other explanation.


texts: Derivative of Gibbs Energy wrt Temperature at constant Internal Energy

texts:
I came across with the following solution from Sandler's book: $$\begin{eqnarray}\left( \frac{\partial G}{\partial T} \right)_U &=& \frac{\partial (G,U)}{\partial (T,U)} \\ &=& \frac{\partial (G,U)}{\partial (T,V)}\cdot \frac{\partial (T,V)}{\partial (T,U)} \\ &=&\frac{(\partial G/\partial T)_V (\partial U/\partial V)_T-(\partial G/\partial V)_T (\partial U/\partial T)_V}{(\partial U/\partial V)_T} \end{eqnarray}$$

Please help me understand these steps. What happens in line 1? I know that line 2 is by using Chain Rule by then how did line 2 becomes line 3?


texts: The reported solubility product of $\ce{HgS}$ is $4 \times 10^{-54}$. How is this possible? The minimum concentration that is possible is 1/avogadro's constant which shall be about $10^{-23}\ \mathrm{M}$. Hence the minimum value of solubility product for a diatomic specie like $\ce{HgS}$ would be about $10^{-46}$. What am I missing?


texts: Explain the structure of HNC (Hydrogen Isocyanide)

texts:
What are the different types of bonds present in the structure?

Does Nitrogen donates one electron from its lone pair to carbon and acquires a positive charge?

How do I determine the Oxidation state of Nitrogen and Carbon?


texts:
Since calcium oxalate is 3000 times less soluble than calcium sulfate, would it be possible to concentrate sulfuric acid from let's say $\pu{50\%}$ solution using following steps? :

adding calcium carbonate to cold dilute $\ce{H2SO4}$
filtering off resulting $\ce{CaSO4}$
mixing $\ce{CaSO4}$ with oxalic acid in 1:1 molar ratio
adding just enough water to submerge the solids
vacuum filtering off the now concentrated (hopefully) $\ce{H2SO4}$

My reasoning behind this is that even though at any given time there's only a small amount of $\ce{CaSO4}$ dissolved, the reaction producing sulfuric acid would eventually go to completion with high yield due to it's the massive kinetic favourability. The only problem I see is that the amount of water needed would limit the final concentration. Would adding merely enough water to wet all the solid still work, improving the final concentration?


texts: Does aqueous component contribute to the equilibrium constant?

texts:
Consider an equilibrium reaction with an aqueous solution $\ce{A(aq)}$ in equilibrium phase with gas:
$$\ce{A(aq) + B(g) <=>[$K_\mathrm{eq}$] C(g)}$$
Would the equilibrium constant have aqueous solution $\ce{A(aq)}$ contributing to it?

In my opinion I think it would. Can anyone please correct me? Also, please help me  find literature which explains equilibrium constant in details.


texts: Why does an electron lose energy so that it falls back to a lower energy state than just stay at the higher energy state?

texts: Suppose an electron in the 2nd shell gets excited and jumps to the 4th shell. Shouldn't the electron then exist in an unstable equilibrium in the 4th shell, than lose energy and drop down to the 2nd shell? What causes it to come out of the equilibrium position and lose energy? The teacher who gave me this problem to think about said that quantum mechanics plays a role in this. Can anyone please give an explanation?


texts: Has a carbon compound ever been found having an ionic bond?

texts: Though it is highly unlikely, has any carbon compound been found to make an ionic bond and to exhibit ionic properties?


texts:
$$\ce{Cr2O7^2-(aq) + 14H+(aq) + 6Cl-(aq) -> 2Cr^3+(aq) + 3I2(aq) + 7H2O(l)}$$

Two chromium atoms gain 3 electrons each. They go from $0$ to $3+$

Similarily, 6 iodine atoms go from $-1$ to $0$, thus gaining one electron. However, my textbook says that iodine has lost electrons. How?

It went from negative to positive, i.e. from $-1$ to $0$, just like chromium from $0$ to $+3$.


texts: Could you suggest me a good coupling method for amide synthesis between tetrahydroisoquinoline and a carboxylic acid?

texts:
I want to synthesize an amide using tetrahydroisoquinoline and an unsaturated carboxylic acid which is light sensitive. I tried using DCC as a coupling agent and DCM as the solvent at room temperature, but it didn't work for me. The tetrahydroisoquinoline is in hydrochlorated form.

Do I have to do acid extraction prior to synthesis, or I can use the hydrochlorated form itself? Please suggest a good method along with the conditions for the reaction to be carried out.


texts: Is it possible to create a salt with multiple anions with only one cation(e.g. CaBrCl)?

texts: I know that usually more electronegative anions would displace less electronegative anions but is there a way to get different anions to "share" a cation?


texts:
We were taught that $\ce{Cr_2O_7^{2-}}$ (dichromate) in $\ce{H_2SO_4}$ gives $\ce{CrO_3}$

$$\ce{Cr_2O_7^{2-} +H_2SO_4 -> CrO_3 + ...}$$

Link: wikipedia

But we know that dichromate in acidic medium converts to $\rm Cr(III)$.

$$\ce{ Cr_2O^{2−}_7 + 14 H3O+ + 6 e− → 2 Cr^{3+} + 7 H2O}$$

Link: wikipedia

How is this possible?


texts: Does sheer amount affect reaction rates?

texts: For example, in the iodine and starch reaction, if I use 20 mL of a set concentration of each, will it be slower to completion if I use 40 mL of each at the same concentration?


texts:
In this video, Steve Spangler says the substance he is using (a polyethylene oxide): http://www.youtube.com/watch?v=m-88M75_PCI

He mentions that one molecule would go to the moon and back twice! I have a hard time believing this, but I guess it must be true.. Is it true that polyethylene molecules can be that long?


texts: Why do you count both bonding electrons towards an atom's octet, but you only count one of them towards the atom's charge?

texts:
For example, oxygen is neutral when it has just 6 electrons. But the pink O in the molecule pictured has 3 bonds giving it 8 electrons, a full-octet. It's more electronegative than all the atoms it's bonded to also. It would make sense if an O with a full-octet had a -2 charge since it has an extra 2 electrons.
But because it "owns" only 1 electron from each bond, the O has a positive charge. This doesn't make sense to me: if we don't count the extra electrons in its charge, why do we count them towards its octet?


texts: When a terminal alkenyl borane is succumbed to halogenation where the halogen and the base are added in two separate steps, the geometry of the double bond is changed. When they are added simultaneously, the double bond geometry is retained. Why is it so?


texts: Can a clay brick waste in a soil be a source of minerals for plants?

texts: Clay brick is made by heating them so their clay structure changes. What i understand is ultimately all materials have one or another base minerals in it particularly here this brick still it remains in some other form. So after process of heat, those minerals or nutrients can remain in such condition a plant can absorb? Can a brick dust be a good source of nutrients for plants to grow?


texts: Rapidly cooling Aluminum vapour to solid state?

texts: What sort of a microstructure would you get on bubbling Aluminium vapors through a large tank of Helium?Would it be a glassy microstructure and/or would you get nano-powders? and/or a new crystal structure formation because of the excess helium which would be present in the aluminium matrix? Ignore metal coolant reactions, if any. Aluminum vapour would consist of Aluminium atoms, unlike liquid aluminum which consists of clusters. So, on rapid cooling from gas to solid, would you still get an FCC crystal structure for aluminium? (There would be no time for diffusion)


texts: Calculating pre-exponential factor using transition state theory

texts:
I would like to calculate the pre-exponential factor of a surface reaction using transition state theory. I've seen two ways to calculate it but I get different answers for each method (and I don't understand why):

$A = \frac {k_b T} {h} \frac {q^{TS}} {q^{reactant}}$ ... (1)

$A = \frac {k_b T} {h} \exp \bigg({\frac {S^{TS} - S^{reactant}} {R}}\bigg)$ ... (2)

where $q^i$ is the partition function of species i, $S^i$ is the entropy of species i, $k_b$ is the Boltzmann constant, $T$ is temperature, $h$ is Planck's constant and $R$ is the molar gas constant.

I assumed the adsorbates only have vibrational contributions to $A$ and the vibrations can be described using the Harmonic approximation.

I am using the following equations to estimate $q^i$ and $S^i$:

$q^i_{vib} = \prod_j^{n_{vib}} \frac {1} {1-\exp \big(- \frac {\Theta_j} {T}\big) }$ ... (3)

$\frac {S^i_{vib}} {R} = \sum_j^{n_{vib}} \frac {\Theta_{V,j}} {T} \frac {\exp \big({- \frac {\Theta_{V, j}}{T}}\big)} {1 - \exp\big( - \frac{\Theta_{V, j}}{T}\big)} - \ln \bigg(1-\exp\big(-\frac{\Theta_{V,j}}{T}\big)\bigg)$ ... (4)

where $n_{vib}$ is the number of vibrational modes, $\Theta_{V,j}$ is the vibrational temperature of a mode (in K).

Inputs

T = 750 K

Reactant $\Theta_V$ in K:

0.42190081

0.08952052

0.08826819

0.06520753

0.05161751

0.05077054

Transition State $\Theta_{V}$ in K:

0.21401905

0.06477819

0.05798548

0.05276798

0.04599558

0.14870034$i$ (Imaginary frequency is ignored)

Results

$A_{eq 1} = 1.61\times 10^{13} s^{-1}$

$A_{eq 2} = 1.36\times 10^{13} s^{-1}$

Intermediate values

$q^{TS} = 9.743$

$q^{reactants} = 9.430$

$\frac {S^{TS}}{R} = 4.93$

$\frac {S^{reactant}} {R} = 5.07$


texts: Mixing naphthalene, formaldehyde and sulfuric acid (Marquis reagent + naphthalene)

texts:
Excuse me if this a dumb question but it has haunted me for years. Back in my old school days I mixed  naphthalene, formaldehyde and sulfuric acid in a mad attempt to make $\mbox{2-Methoxynaphthalene}$. I can't remember if I heated the mixture or not.

It turned black instantly and my teacher at school couldn't tell me what had happened, even less why. Did I produce nano-carbon? Just soot? Or something else?

Edit:
way back then, I did try the reaction without naphthalene, and also without formaldehyde, with no (noticeable) result. My teacher also repeated the experiment with the considerably more pure chemicals available at the school lab.

Edit2: as of the comment by Loong, what I did was using Marquis reagent on naphthalene. What I found on the net about this was very little and poor. I couldn't even find anything on the color of $\mbox{polymethylnaphthene}$. (Instinct tells me it should be colorless.)


texts:
What's the difference between the two molecules? I can always read about β-D-fructofuranose in the chemistry books, but unfortunately, I've never found any info concerning β-D-fructopyranose. Is there a big difference between them (apart from their ring structure)?
And where can the furanose and the pyranose form be found in nature?


texts: How can I make a lot of microscopic rods of metal?

texts:
I want to make around 40-200 g  of metal cylinders that would ideally have a length of around 1-100 μm in size (smaller preferred). The rods will be made of some ferromagnetic material such as Iron or Nickel.
The reason for this is to make a magnetic field display where the tiny metal rods are submersed in a viscous liquid which is trapped between two clear sheets of material (likely glass or acrylic).
Since these are rods and not balls, this should allow them to stick end to end without bunching up so much and better visualise the magnetic field lines.
Although i'd prefer The rods to be smooth, they don't necessarily have to be a cylinder shape, they just have to have a length to width ratio higher than 2:1 (although i'd prefer a bigger aspect ratio than that).
It is preferred, but not necessary that the rods are all the same length with minimal variation in size.
Last preference is for the metal to look shiny rather than black as this helps a lot with visualising the field lines. I'll take what I can get though.
Haven't found anything online like this but I also don't really know what to search for.
I thought of using thin iron/steel wire and cutting it up but this process would most likely be too difficult and tedious to carry out unless I could construct some machine or jig to do it for me. I also have struggled to find any sort of ferromagnetic wire smaller than 0.1mm which would still be too thick for what I want.
I also thought of long metal shavings but they tend to be twisted and irregular (and possibly too flat) to work well for this.
Perhaps I could use some sort of micro 'cheese grater' to grate pieces off of a metal block?
Could these rods be synthesized via electrolysis somehow?
I'm at a loss so any help or pointers on how to go about this would be greatly appreciated!


texts: Can you write (with and ink pen) on hydrophobic paper?

texts: Would the ink be repelled from the paper or prone to smearing?


texts: Calculating new volume during expansion of an ideal gas

texts:
Question
  $\mathrm{5~mol}$ of a gas is confined in a piston (volume $\mathrm{100~cm^3}$) at $\mathrm{400~K}$. $\mathrm{10~kJ}$ of heat energy is supplied, causing a reversible and isothermal expansion of the gas. Calculate the volume of the expanded, heated, gas. You may use the equation below (assume ideal gas behaviour).

  $$W = -nRT(\ln V_2-\ln V_1)$$

I substituted the values (after converting to SI units) into the equation and attempted to rearrange to find $V_2$, but work was unknown. I tried to use the enthalpy value (10 kJ) given but I was unsure of what to do with it.


texts: Understanding the hybridization of cyclohexane?

texts:
I'm having quite a fair bit of trouble comprehending the hybridization of cyclohexane. I understand that this is a ringed structure with single C-C bonds, therefore all the carbons should have sp3 hybridization right?

Apparently however, this is incorrect, but I am not sure why. I'm reading about how it not planar like benzene is, and adopts a chair/boat conformation which I am having trouble visualizing as well.

If someone could provide some insight on this topic, that would be great!


texts:
This is the NMR for the molecule shown. I was told that carboxy group will be in the above 10ppm range. Does that tiny signal at about 12.9 ppm indicate the carboxy group though? I dont understand why the methoxy would show large integration while carboxy barely shows.
Also my general question is, how much absorption is necessary for it to indicate some group present?  Is there "noise" on NMR spectra or does every signal indicate a group?


texts: will mercury vaporize in boiling water in a flask?

texts:
Will mercury vaporize with the water vapours if boiled in a flask full of water?

Also if we store mercury under water in the beaker will it still give vapours?

If some mercury is bound to vaporize , will there be any mercuric oxide formation or not ??


texts: Will entropy increase in adiabatic expansion?

texts:
The formula for entropy change states that change in entropy is not possible if heat change is nil.
∆S=∆Q/T
But what if we adiabatically expand a gas? Won't the molecules get more space to vibrate in, hence increasing the randomness of the system, therefore increasing the entropy?


texts: Questions about van't Hoff factor in colligative property

texts:
I learned from many websites that $i$ of strong acids and bases and some weak bases could be determined by how many ions are dissociated. But, I realized that I need to calculate the $n$ in $i=1+(n-1)a$ ($a$ is the degree of dissociation), not the $i$ in my problems.

Is there any rule to calculate the $n$ for strong acids and bases and weak acids and bases? Do I also need to check solubility table to solve colligative property problems that using van't Hoff factor?


texts: What is the difference in mosM and mOsm units, if there is any at all?

texts:
I'm reading Agre's paper on aquaporins [1] and he uses a unit called "mosM" throughout the paper, for example:

… ocytes were transferred from 200 mosM to 70 mosM modified Barth's buffer.

I just want to understand what this unit means, is it the same as mOsm? I know this might be an very stupid question but hey, I'm only a undergrad.
Reference

Preston, G. M.; Carroll, T. P.; Guggino, W. B.; Agre, P. Appearance of Water Channels in Xenopus Oocytes Expressing Red Cell CHIP28 Protein. Science 1992, 256 (5055), 385–387. DOI: 10.1126/science.256.5055.385.


texts: Entropy Change for mixing water at two different temperatures

texts:
Assume that the heat capacity of water is independent of the temperature.  Calculate the net entropy change when 1 mole of water at 0 degrees Celsius is mixed with 1 mole of water at 100 degrees Celsius. Assume that the heat capacity of water is (4.184 J/(K-g))(18 g/mol) = 75.3 J/(K-mol) and that the heat capacity of the calorimeter is negligible.

I was wondering if the following general methodology of my attempt was correct.

In attempting to solve this, I first found that the equilibrium temperature was (273+373)/2 = 323 K.

Then, I calculated the entropy by using the equation S = (heat capacity)*ln(T_eq/T_initial) for both 0 degrees and 100 degrees.

Afterwards, I added the two values for entropy and obtained 1.827 J/(mol-K) as the answer.

.


texts: Why is 2-fluorobenzoic acid more acidic than 4-fluorobenzoic acid despite its intramolecular hydrogen bonding?

texts:
I was reading about $\mathrm{p}K_\mathrm{a}$ values of 2-fluorobenzoic acid and 4-fluorobenzoic acid and found that the latter had a higher value which was surprising to me. I think that intramolecular hydrogen bonding should dominate all the other effects in 2-fluorobenzoic acid as mentioned in the following figure and thus it should have a higher value:

What is wrong with my logic?


texts: Does formal charge affect bond polarity?

texts:
Bond polarity, as far as I understand, is a measure of the degree  to which shared electron density is distorted, and thus solely depends on the electronegativity difference.
Up until now, I had learnt that the dipole moment (charge on each atom x separation) is used as a measure of the polarity. However, for molecules with a formal charge like CO, even though the shared electron density is distorted towards the more electronegative atom, the dipole moment points in the opposite direction. For other molecules like Ozone, even though there is approximately no distortion of bonding electron density, the formal charges alone result in a dipole moment.
For a general molecule, am I supposed to take into account the formal charges for bond and thus molecule polarity, and it it even a measure of degree of distortion/ionic character at that point?


texts: When we add soap in low concentrations to water it reduces the surface tension. Why? What is the purpose of this?

texts: I understand how soaps lower the surface tension of water but I don't know what the purpose of this is. How does this help with cleaning, removing stains etc?


texts:
I don't know what identical molecules are but these are by thoughts.

Since from the word identical the molecules should have the same number and kind of atoms attached in the same way. Since in stereo-chemistry the isomerism is due to spacial orientation all stereo-chemical isomers are identical.

Is my thinking correct? What factors determine whether two molecules are identical or not?


texts: Why does reduced mass help when talking about two body problems?

texts:
Firstly I would like to say that despite the fact that you may be thinking that this is a physics question and should probably be asked on that part of the website, I came across reduced mass for the first time in Chemistry - physical and inorganic - and it is used a lot in Chemistry so I thought it suitable for this part of the site.

With that said, I will now elaborate on my question. I hear people say that reduced mass ,$\mu$, is used for two body problems, but what sort of problems? Is it so that the two body system can be treated as one body or is it to simplify calculations regarding how the two bodies act upon each other?

I can follow the derivation (which I shall go through shortly) in a mathematical sense but I can seem to be able to grasp the ideas behind why the steps were taken.

Derivation:

Step [1] - From Newton's laws of motion: $$F_{12}=-F_{21}$$ It follows that: $$m_1a_1=-m_2a_2$$
Step [2] - Simple rearrangement of the result from step 1 to make $a_1$ the subject (it seems a reasonable thing to do but I don't know why it's done). $$a_1=-\frac{m_2}{m_1}a_2$$
Step [3] - The relative acceleration, $a_{rel}$, can be found by subtracting the acceleration of one body from the other (I get how this is done and get that it would give the relative acceleration BUT I don't know why you would need the relative acceleration). $$a_{rel}=a_1-a_2=(1+\frac{m_1}{m_2})a_1=\frac{m_2+m_1}{m_1m_2}m_1a_1=\frac{m_2+m_1}{m_1m_2}F_{12}$$
Step [4] - According to Wikipedia the result from the last step can be used thus (I have no idea what's going on in this step):
$$\frac{m_2+m_1}{m_1m_2}F_{12}=\frac{F_{12}}{\mu}$$ Thus: $$\mu=\frac{m_1m_2}{m_2+m_1}$$

Again, I can do the maths but my problem here is conceptual I believe. I have included the derivation in my question because I believe that it's possible that if you were able to shed some light on why particular steps were taken that this may help.


texts: How quickly will steel lose structural strength from a heat flash?

texts:
I want to know if a sustained jet fuel burn around steel has the ability to make the steel structurally unsound. It seems like any applied heat that effects steel will be a kind of "heat flash": a sudden, and possibly quite short-lived, burst of heat. In this situation, we assume steel has a melting point of $\mathrm{2750\ ^\circ F\ (1510\ ^\circ C)}$ and that jet fuel (the source of the heat burst) burns at a maximum of $\mathrm{1500\ ^\circ F\ (\approx 816\ ^\circ C)}$.

Some factors I believe need to be taken into place include the strength of bonds in steel, the thickness of the steel in question, and the distance from the heat source. Is a sudden heat flash enough to cause steel to weaken? Are there any other factors that need to be taken into consideration?


texts:
How many stereoisomers are possible for the compound in picture? I'm getting 8. Is that correct?

My approach was as follows: The left hand methyl groups may be both up or one up and one down. For each of these cases the groups on the right may be in $(E{,}Z'),(E'{,}Z),(E{,}E'),(Z{,}Z')$ configurations. So $4\cdot2=8$.

I think it is quite evident that carbon having 2 π bonds must be linear. I apologize for the non-linearity in the picture. I hope you will be able to understand the question otherwise.


texts: How do the fields of medicinal chemistry, pharmaceutical chemistry, pharmacy, and pharmacology differ?

texts:
I would like to know what the difference between medicinal chemistry, pharmaceutical chemistry,  pharmacy and pharmacology. All of them seem to involve the development of drugs, so I am confusd as to how to distinguish them.

Also, does specialising in medicinal chemistry require a biology background? It seems to lean more towards biology.


texts: Can someone explain the equation for entropy?

texts:
Here's the equation:

$\Delta S = \frac{\Delta q}{T}$

The confusion I have with this equation lies in the variable for temperature, $T$.  Why is the temperature constant in this equation? Why can't the equation include $\Delta T$ instead of just $T$ and, surely, if $\Delta q$ is negative or positive the temperature must decrease or increase, respectively.


texts:
What does phase mean in orbitals?

I know that phases are separated by nodes. They are in some way related to wavefunctions, I can't understand, how? How can wavefunctions be negative, since they are complex numbers (as I know)?


texts: Why is carbon dioxide bent in its first excited state?

texts:
R. H. Crabtree writes in The Organometallic Chemistry of the Transition Metals (p 145, 6th ed.) that

  $\ce{CO2}$ is linear in the free state but bent [...] in the first excited state...

Why is this so? (The context refers to an electronically excited state.)


texts: Reaction of Diols with HX hydrohalic acids, Competing SN2 Reactions

texts:
Suppose 1,5-pentanediol were exposed to something like hydroiodic acid. Would the alkoxonium end of the diol be exposed to a nucleophilic attack by the remaining hydroxide at the other end for a ring formation? Or would the newly-free iodide ion be more competitive for substitution? Thanks!

edit: It was pointed out to me "newly-free iodide" was quite confusing. I meant it as though HI dissociated, the Hydrogen ion attacked one end of the diol, and the iodide from the HI being "newly-free". Now that one end of the diol has a good leaving group (H2O), is it more susceptible to be attacked by the iodide, or by the other end (OH) of the diol.


texts: Why is water not part of the equilibrium constant?

texts:
In the acid base reaction
$$\ce{NH4+ + H2O <-> NH3 + H3O+}$$

the acidity constant, which is a relation between concentrations is given by
$$K_{\mathrm{a}}=\frac {\ce{[NH3]} \cdot \ce{[H3O+]}}{\ce{[NH4+]} \cdot \ce{[H2O]}}$$

Since $\ce{[H2O]}$ is constant, it can be included inside the constant to obtain a new $K_\mathrm{a}$ which is $6.3 \times 10^{-10}$.

(Being a constant allows us to relate the molar concentration to the density of water.)

And so, even though some quantity of water reacts with $\ce{NH4+}$, but the volume of water varies in a way that $\ce{[H2O]}$ would still be constant.

What I don't understand is why the molar concentration of water is constant. Why isn't it handled the same way as the other reactant?
I understand that if $\ce{H2O}$ was the only liquid and the rest of the reactants and products were of different state (gaseous or solid), then water would exist alone in the beaker and its concentration would therefore remain constant, but this is not the case.

That was about heterogeneousness. Trying another guess; in the reaction of esterification $$\ce{{alcohol} + {carboxylic acid} <-> {ester} + H2O}$$
$\ce{H2O}$ is considered as a product which concentration is not constant, so it is counted explicitly in the equilibrium constant.

Could the answer be that $\ce{NH4+}$, $\ce{NH3}$ and $\ce{H3O+}$ are dissolved in water, while the alcohol, the carboxylic acid, and the ester are not?

I'm looking for an answer that clearly shows which volume is considered (water or the solution), because I'm confused as to why something would or wouldn't be included in the equilibrium constant.


texts: What is the diffusion limiting current density in comparison to rotating electrodes or fuel cells with pumps/stirrers?

texts: If an electrolytic fuel cell operates in an acidic liquid electrolyte and electrons are supplied to a catalytic electrode so that the protons in the liquid solution will react and produce hydrogen gas, how much is the performance of the fuel cell limited by letting the protons simply diffuse onto the catalyst instead of rotating the electrode or stirring the liquid? I read about diffusion limiting current density but I wonder whether practically, fuel cells operating based on simple molecular passive diffusion are extremely inefficient. Can you give me a difference in magnitude between the current density of a fuel cell based on passive diffusion and a fuel cell based on rotating electrode or stirring? Is it 2 times higher or 2,000 times higher etc?


texts:
Can you make a supersaturated gas solution?
As we know solubility decreases when we increase the temperature, So If I do that, will the gas molecules escape the solution or will they stay in the solution and make a supersaturated solution? Or is it just a plain fact that you can't make supersaturated solutions except with solids solutes?

I am kind of leaning towards escaping, because it is hard to keep gas molecules intact with water molecules at high temperatures.


texts: Action of hot alkaline KMnO4 on tert butyl benzene

texts: Side chain oxidation of aryl alkanes takes place if there is at least one alpha hydrogen present by all accounts I presumed that there would be no reaction. However the answer given was trimethyl acetic acid. Is the answer key wrong?


texts: Meaning of 1,1,1,2 in 1,1,1,2-Tetrafluoroethane & similar

texts:
What is the meaning of the 1,1,1,2 part in the compound 1,1,1,2-Tetrafluoroethane, a refrigerant commonly known as R-134a, some info:
Formula: $\ce{CH_2FCF_3}$
Structure:

Reference: http://en.wikipedia.org/wiki/1,1,1,2-Tetrafluoroethane


texts: Enthalpy of reaction between ammonia and oxygen

texts:
I have to ask this here because I asked literally everybody I know and I still disagree with them.

  Using the information in the table below, calculate the heat of released from the following reaction in $\pu{kJ}$ per $\pu{g}$ of $\ce{NO}.$ (Mw. of $\ce{NO}$ is $\pu{30.01 g/mol})$

  $$\ce{4 NH3(g) + 5 O2(g) -> 6 H2O(g) + 4 NO(g)}$$

  $$
\begin{array}{lrrr}
\hline
  & \ce{NH3} & \ce{H2O} & \ce{NO} \\
\hline
H_\mathrm{f}^\circ~(\pu{kJ/mol}) & -46.1 & -241.8 & +90.3 \\
\hline
\end{array}
$$

  a) $-13.29$
  b) $-8.372$
  c) $-7.541$
  d) $-30.16$
  e) $-5.678$

I'm convinced the answer is c.

The enthalpy of this reaction for 4 moles of NO is -905.2, to find the enthalpy for 1 mole of NO we have to divide by 4 to get to -226.3.

Then, to find it per gram of NO we have to divide by 30.01, this gives us 7.541.

Am I right ? If not, what did I do that was wrong? Where's my mistake?

Please don't put this as HW help, I asked multiple websites and went through my working 5-6 times but I still couldn't point out where I went wrong.


texts: How to rationalise the resonance structures of nitrogen dioxide?

texts:
The following image depicts resonance in $\ce{NO2}$ molecule:

I don't know if it is obvious or not, but I'm puzzled by this structure. I've read about the structure of the $\ce{NO2}$ compound, but it wasn't related.
In the first structure, nitrogen is having a single electron with a positive charge, and oxygen is having a negative charge. So, that means nitrogen has donated a single electron to Oxygen, without forming a bond. I know it can be possible, but I couldn't understand how it happens.
Also, I thought that nitrogen donates a lone pair to oxygen, as it can have a maximum co-valency of 4. As in the following image:

But, this isn't the case here. Why?


texts: According to Ahn.N.T "Frontier Orbitals" hydroboration isn't a pericyclic reaction because boron uses two AOs and not one. The same applies for cheletropic reactions, which aren't pericyclic either. But the IUPAC goldbook says different: http://goldbook.iupac.org/P04491.html - that cheletropic reactions are pericyclic. So is hydroboration, too?


texts: Why are antibonding molecular orbitals formed?

texts: When two atomic orbitals make one molecular orbital there must be an antibonding orbital also. Why should they make also an antibonding molecular orbital, such as the $2\mathrm b_2$ orbital in the scheme below?


texts: When can a molecule be considered freely rotating at room temperature?

texts:
This question sparked from a long discussion in chat about the nature of $\ce{H2O2}$ and whether that molecule can be considered to rotate around the $\ce{O-O}$ axis (and hence display axial chirality) or not.

Considering two rather clear cases:
Ethane is considered to rotate freely around the $\ce{C-C}$ bond. The activation energy for rotation (equivalent to the energy difference between the staggered and eclipsed conformations) is given as $12.5\,\mathrm{\frac{kJ}{mol}}$.

Ethene on the other hand is considered to not freely rotate around the $\ce{C=C}$ bond. The energy difference between the planar and perpendicular conformations (the rotation barrier) is given at $250\,\mathrm{\frac{kJ}{mol}}$. (I am unsure of this value which I found on Yahoo answers. If I understand correctly, this should correspond with the excitation from $\unicode[Times]{x3C0}$ to $\unicode[Times]{x3C0}^*$ which I found elsewhere as $743\,\mathrm{\frac{kJ}{mol}}$.)

Somewhere between these two extreme cases must lie some kind of barrier around which rotation is severely hindered to entirely inhibited.

Attempting to calculate this myself, I remembered the Boltzmann distribution: If two states differ in energy by $\Delta E$, their relative populations $F_1$ and $F_2$ can be calculated as follows:

$$\frac{F_2}{F_1} = \mathrm{e}^{-\frac{\Delta E}{k_{\mathrm{B}} T}}$$

($F_2$ being the higher energy state and $k_\mathrm{B}$ being the Boltzmann constant.)

If I calculate relative populations from the energy differences $12.5, 19, 25$ and $250\,\mathrm{\frac{kJ}{mol}}$ for ethane, butane, $\ce{H2O2}$ and ethene, respectively (which correspond to $0.13, 0.20, 0.26$ and $2.6\,\mathrm{\frac{eV}{particle}}$) I get the following results at $300\,\mathrm{K}$:

Ethane: $6.55 \times 10^{-3}$
Butane: $4.79 \times 10^{-4}$
$\ce{H2O2}$: $4.29 \times 10^{-5}$
Ethene: $2.09 \times 10^{-44}$

Or logarithmic (ln) values of:

Ethane: $5.03$
Butane: $7.64$
$\ce{H2O2}$: $10.1$
Ethene: $101$

Again, somewhere between butane and ethene must be a threshold-ish value, above which free rotation at $300\,\mathrm{K}$ cannot be considered, but what range are we looking at; similar to what energy difference does this correspond to?

Asked the other way round, if I have an energy barrier of $25\,\mathrm{\frac{kJ}{mol}}$, what would I need to put on into the equation to calculate the temperature above which free rotation can be assumed?


texts: Why do acids mix in water faster than bases?

texts:
I have $100\ \mathrm{L}$ of water in a tank with an mixer inside and want to know how fast the tank mixes at a given rpm-setting.
I am adding $50\ \mathrm{mL}$ of $2\ \mathrm{N}\ \ce{HCl}$ and see how long the $\ce{pH}$ goes to down to an equilibrium.
Then I add $50\ \mathrm{mL}$ of $2\ \mathrm{N}\ \ce{NaOH}$ to the solution and wait for the $\ce{pH}$ to come to an equilibrium $\ce{pH}$.
I feel like the 2 times should be the same, but acid mixes much faster than base in all cases. Why?

The time for $\ce{pH}$ to change from $7$ to $4$ is always less than time for $\ce{pH}$ to change from $4$ to $7$ in the same tank at the same rpm.

Any theories regarding why?


texts: A bonus question would be, if so, why? Is it because it decomposes and hence the expiry date is calculated out?


texts: Why are DCM and chloroform so resistant towards nucleophilic substitution?

texts:
In the book Organic Chemistry by  J. Clayden, N. Greeves, S. Warren, and P. Wothers I found the following reasoning:

  You may have wondered why it is that, while methyl chloride (chloromethane) is a reactive electrophile that takes part readily in substitution reactions, dichloromethane (DCM) is so unreactive that it can be used as a solvent in which substitution reactions of,other alkyl halides take place. You may think that this is a steric effect: Indeed, $\ce{Cl}$ is bigger than $\ce{H}$.
  But $\ce{CH2Cl2}$ is much less reactive as an electrophile than ethyl chloride or propyl chloride: there must be more to its unreactivity. And there is: Dichloromethane benefits from a sort of 'permanent anomeric effect.' One lone pair of each chlorine is always anti-periplanar to the other $\ce{C–Cl}$ bond so
  that there is always stabilization from this effect.

So, in MO-terms the situation would look something like this.

The reasoning looks plausible to me. The interaction between the free electron pair on $\ce{Cl}$ and the $\sigma^{*}$ orbital of the neighboring $\ce{C-Cl}$ bond, which would be the LUMO of DCM, lowers the energy of the free-electron-pair-orbital, thus stabilizing the compound and it raises the energy of the LUMO, thus making DCM less reactive towards nucleophiles.

But how important is this anomeric effect actually for explaining the unreactiveness of DCM toward nucleophiles, especially compared to the steric effect? And how important is the steric effect actually: Is the steric hindrance exerted by the second $\ce{Cl}$ in $\ce{CH2Cl2}$ really that much larger than the steric hindrance exerted by the methyl group in $\ce{CH3CH2Cl}$ (which is a good electrophile for $\mathrm{S_N2}$ reactions)?

I'm a little skeptical because if this anomeric effect was very important I would have expected that the $\ce{C-Cl}$ bond length in DCM would be slightly higher than in methyl chloride because there should be some transfer of electron density from the free electron pair into the antibonding $\sigma^{*}$ orbital, which should weaken the $\ce{C-Cl}$ bond. But the actual bond lengths don't show this. They show rather the contrary:

$$\begin{array}{c|c}
\hline
\text{Species} & \text{Average }\ce{C-Cl}\text{ bond length / Å} \\
\hline
\ce{CH3Cl} & 1.783 \\
\ce{CH2Cl2} & 1.772 \\
\ce{CHCl3} & 1.767 \\
\ce{CCl4} & 1.766 \\
\hline
\end{array}
$$
(source: Wikipedia)

Now, I know that the stronger polarization of the $\ce{C}$ atomic orbitals in di-, tri-, and tetrachlorinated methane as compared to methyl chloride (due to the electronegativity of $\ce{Cl}$) should lead to an overall strengthening of the $\ce{C-Cl}$ bonds in those compounds. But I would have expected a trend that would show only a slight decrease (or maybe even an increase) of bond length when going from methyl chloride to DCM and then a more pronounced decrease when going from DCM to chloroform followed by a similar decrease when going from chloroform to tetrachloromethane. But instead the polarization effect seems to only slightly increase on adding more chlorine atoms.


texts: Basic chemistry of the Shinoda test for flavonoids?

texts:
In this test, four pieces of magnesium fillings (ribbon) are added to the ethanolic extract followed by a few drops of concentrated hydrochloric acid. A reddish colour indicates the presence of flavonoid.

What is the basic chemistry of the test?  What are the chemical reactions taking place in the test that lead to the formation of red precipitate, and also, why have we used magnesium and concentrated HCl in the test?


texts: Experimental measurement on the ring-strain

texts:
for my thesis i calculated the ring-strain of a molecule by MP2 on the computer. I was wondering if there is an easy possibility to get the experimental value of the ring strain. I guess I have to combust the compound and somehow calculate it from the combustion-enthalpy. My Problem is, that there is no access to the open form of the molecule to compare it. Is there still a way to calculate it?
I thought of the Hess-law maybe there is a way with some standard values?
It is an organic molecule only containing C, H and O.


texts: Concentrating Oxalic Acid by Evaporation

texts:
I bought Oxalic Acid in an aqueous solution from a hardware store years ago. I need to turn it to powder form for easier storage and other things.

Can I simply evaporate the solution? I seem to notice that evaporating it releases fumes that are similar when one is boiling Acetic Acid. Are there more Oxalic Acid being lost just as it is when boiling Acetic Acid (not distillation)


texts: Alternatives to Bayer process for extracting aluminum from lunar regolith

texts: I am exploring ways to produce metallic aluminum from lunar regolith. According to most published results of lunar soil, $\ce{ Al2O3}$ comprises roughly 14% of mare samples by mass with $\ce{SiO2}$ being main impurity (40%). From what I been able to understand so far, both Bayer and Serpeck’s processes rely on reagents that can't be produced in-situ. Hence, the challenge is to use the least amount of chemistry to refine lunar material to the point when electrolysis can be used. Maybe magnetic separation?  Is Al2O3 (aluminum oxide) diamagnetic or paramagnetic?


texts: Combustibility of gas/carbon dioxide mix

texts: Via electrolysis I produced an ethane/hydrogen/carbon dioxide mix. Normally, there is 1 part ethane, 1 part hydrogen and 2 parts carbon dioxide. If I simply used a Bunsen burner with air hole closed to try to burn this gas, would it burn at all? Would the hydrogen burn properly but the ethane produce lots of soot and carbon monoxide?


texts: UV Absorption of iodine with some solvent

texts:
$I_2$ in solution is typically absorbing around $525 \; nm$ this is why it appear to be magenta, I recently learn that with some solvent :

Benzene
Toluene
$o$-Xylene
$p$-Xylene

The coordination complex between the solvent and $I_2$ is also absorbing around $300 \; nm$ I guess there is some explanation with the MO diagram ?


texts: CO stretching frequency band in the IR spectrum for tetracarbonylnickel and tetracarbonylferrate(II)

texts:
A past exam question says:

  With reference to the main bonding interactions between a transition
  metal and a terminal $\ce{CO}$ ligand, explain whether you would expect to
  observe a lower $\ce{CO}$ stretching frequency band in the infrared
  spectrum for $\ce{[Ni(CO)4]}$ or for $\ce{[Fe(CO)4]^{2-}}$

My attempt at an answer is:

  There are essentially two bonding interactions at play in the carbonyl
  ligand: a ligand-to-metal $\ce{n → d\sigma}$ interaction and a
  metal-to-ligand ${d\pi → \pi^*}$ interaction. The latter interaction is
  called backbonding, because the metal donates electron density back to
  the ligand.

Nickel is further right in the periodic table than Iron, so $\ce{[Ni(CO)4]}$ has a greater stretching frequency (a greater $\ce{C–O}$ bond order). This is due to the periodic trend in orbital energy. As we move left to right across the periodic table, the $\ce{d}$ orbital energies decrease and the energies of the $\ce{d\pi}$ and ${d\pi^*}$ orbitals separate. As a result, the backbonding orbital interaction is worse in  $\ce{[Fe(CO)4]^{2-}}$ (as strong orbital interactions require well-matched orbital energies)." This means that the ${\pi^*}$-orbitals of the $\ce{CO}$ ligands are significantly more populated in $\ce{[Fe(CO)4]^{2-}}$, so the $\ce{CO}$ bond is accordingly weakened and $\ce{v(CO)}$ is reduced.

Is this correct?


texts:
In very high pressure environments such as mud circulating systems, conditions for polymers contain fugacity/z-compressability criteria instead of Gibbs free energy, more in the answer. So

When fugacity and z-compressability equations instead of Gibbs free energy equations?

and helper questions to the latter

  when are fugacity and z-compressability equations used?
  When are Gibbs free energy equations used?
  By which criteria can you justify your decision to choose between Gibbs free energy criterion and fugacity/compressability criterion?


texts: How to find the oxidation number of Co and Cr in [Co(NH3)6] [Cr(C2O4)3]?

texts: In the question I actually got I had to name the above compound, and I know how to name it but I don't know how to find the oxidation number of the above compound(which has to be mentioned in the IUPAC name). I actually know how to find the oxidation number in complexes but here both the ions are complex ions which makes it confusing. If someone needs the name its Hexaamminecobalt(?) trioxalatochromate(?)


texts:
So, I have $\ce{Cr2O7^2-(aq) + 14 H+(aq) + 6 I-(aq) -> 2 Cr^3+(aq) + 3 I2(s) + 7 H2O(l)}$

and I know the concentrations to be like so:

$\ce{[Cr2O7^2-]}= 1.6\ \mathrm M$

$\ce{[H+]}= 2\ \mathrm M$

$\ce{[I-]}= 1.6\ \mathrm M$

$\ce{[Cr^3+]}= \pu{0.05271 M}$

And I want to calculate the $E(25\ \mathrm{^{\circ}C})$ of this galvanic process.

I know that I have to use $E=E^{\circ}-\frac{RT}{nF}\ln Q $, but I have a few questions:

How can I find $E^{\circ}$?
I know that $n$ represents the amount of electrons moles moving per mole of transformed material, but how can I find it when I have only the complete reaction like here?
With $Q=\ce{\frac{[Cr^{3+}]^2}{[H^+]^14[I^-]^6[Cr_2O_7^{2-}]}}$
I get $Q=\pu{6.32*10^{-9}V}$, which is very very small - does this seem to be the correct $Q$ for $\ln Q$?


texts: Does excessive sulfuric acid as catalyst affect the synthesis of aspirin?

texts:
Recently had a lab experiment to synthesize aspirin.
I was instructed to add 4 drops of concentrated sulfuric acid but misread the "4 drops" as "4 ml".
Ended up with a yield of just 10 %. But the crystals that I obtained upon recrystallisaion weren't of aspirin but of salicylic acid (as confirmed by a melting point of 160 °C).

Did the addition of excessive sulfuric acid affect this in any way? What could have caused salicylic acid crystals to be produced instead of aspirin?

Some technical details of the steps I took:

mixing 2 g of salicylic acid with 5ml of acetic anhydride
4 ml of sulfuric acid added as catalyst (should've been 4 drops)
Heated the mixture in a water bath for 15 min.
Added 1 ml of cold water slowly then added 20 ml of cold water again quickly and stirred for 5 min.
Allowed solution to cool at room temp.
Crude product was dissolved in 5 ml of ethanol. (I noticed that my crude product was able to dissolve immediately whereas my peers' had to heat theirs and took awhile to dissolve, any reason for this?)
30 ml of hot distilled water was added to the mixture and heated on a hotplate.
Allowed solution to cool to room temperature then placed in an ice-bath for 15 min.
Crystals collection by suction filtration.
Crystals were dried in the oven at 100 °C for 15 min.
Crystals placed in desiccator for 10 min.
Melting point of crystals were found to be 159–161 °C


texts: Weird Wikipedia Section on Oxidizing Behavior of Nitric and Sulfuric Acids

texts:
It has been my understanding that when nitric, perchloric, or sulfuric acids act as oxidizing agents, they must exist as whole $\ce{HNO_3}$ or $\ce{HClO_4}$ or $\ce{H_2SO_4}$ molecules that are still protonated. For example, putting copper in dilute sulfuric acid does nothing, but using concentrated sulfuric acid does cause a redox reaction. This agrees with the fact that only concentrated forms of these acids can oxidize; only concentrated forms have undissociated/whole molecules. A dilute solution would contain mostly hydronium and the conjugate base of the strong acid, thus not be able to oxidize. However, the "General Properties" section of this Wikipedia article flat out contradict that.
It says,

However, even dilute nitric acid can oxidize copper to $\ce{Cu^{2+}}$ ions, with the nitrate ions acting as the effective oxidant. (Emphasis: nitrate ions).

Then below it says that concentration is a factor for sulfuric acid. Is something amiss here?

UPDATE: I now embrace what user @matt_black is saying, and by now
I'm not even surprised that something like this could happen. Chemical guidelines are just guidelines. However, I'm now even more curious as to this departure from the trend. If he or someone else would like to give an explanation of the mechanism of reactions involving oxidation (of copper, for instance) by $\ce{HNO_3}$ and $\ce{H_2SO_4}$ that accounts for this anomaly, that would be great.


texts: Reason for inability to find the absolute value of internal energy

texts:
Today in my thermodynamics lecture, my teacher told me that it is not possible to find the absolute value of internal energy and so we have to calculate the change in internal energy.
So, my question is why isn't it possible to find the absolute value of internal energy? Is this statement true?


texts: Solubility of Organic Compound confusion

texts:
My teacher wrote the following on the board today:

  A solute will only dissolve if the energy required to break the bonds
  in the solute and solvent is less than the energy released from the
  bonds formed between the solute and solvent.

I am aware that "like dissolves like" but not entirely sure what the sentence above means.

From the bond enthalpy chapter I learnt that, in an exothermic reaction the bonds formed are stronger due to lower in energy and thus more stable. Although I am not sure whether this is related to solubility, it seems to me that they are contradictory.

So can someone explain to my as to why bonds formed has less energy released than the broken bonds?


texts: How to think about absorption and emission rates and intensity for stimulated emission?

texts:
I learned Fermi's Golden Rule applied to absorption and stimulated emission and encountered the following question:
Since absorption and emission rates are the same for stimulated emission, why can't we say that the incident beam is not attenuated by the sample?


texts: How to draw a photoelectron spectrum with ionization energies?

texts:
I understand the basic concepts of the photoelectron spectrum. However, say I am instructed to draw the PES graph for Silicon. I know how to figure out the relative peaks based on its configuration. But when arranging them on the graph, how can I accurately place them where they should be in ionization energy? That is, the x-axis is labeled 300.0, 200.0, 100.0, etc. Without any other information (and the usage of a periodic table only) how do I know where to put the peaks among the increments? Is there a way to figure out the ionization energies for each peak?

If this is NOT possible, please explain why.


texts:
What does

  $\ce{Pb(NO3)2 + KI}$

form?


texts:
Some chemicals certainly have extraordinary properties. One can consider them extreme in a sense, that they are the prime example for a concept, or they achieve the highest or lowest values in a certain area.

This Q&A attempts to compile a list of questions asked on this network, which have a background related to such extreme values or properties. we decided to add such a list because it is a popular search term.

It is a community effort, hence everybody with more than 100 reputation points can edit the answer. If you think something is missing in this list, just go ahead and add it. This post will be locked to prevent adding new answers, though. The corresponding discussion can be found on meta.chemistry.se. If you think there are some obvious points missing here, please go there and open a discussion.


texts: Green deposition on the anode after electrolysis of sodium bicarbonate solution in tap water

texts:
I use $\pu{12 V}$ battery with copper wires and tap water with $\ce{NaHCO3}$ dissolved in it. I connected the battery and everything went as expected but after 5 minutes bubbling stopped. I took out the copper electrodes and saw green deposits on the anode that were blocking the current.
I think green stuff was malachite formed by the reaction
$$\ce{2 Cu + O2 + H2O + CO2 -> Cu2(OH)2CO3}$$
because there is oxygen in the anode water in solution copper in the wire but how did the $\ce{CO2}$ get there? I know bicarbonates hydrolyze to give carbonic acid which gives $\ce{CO2}$ but doesn't that only happen at the surface? Any ideas what that green thing might be?


texts: Comparing Acidic Strength of H3PO4 and H3AsO4

texts: The $\mathrm{p}K_\mathrm{a}$ values for $\ce{H3AsO4}$ and $\ce{H3PO4}$ are $2.30$ and $2.12$ which indicate that $\ce{H3PO4}$ is a stronger acid compared to $\ce{H3AsO4}$. I looked up their electronegativity values to find that they are almost the same for both arsenic and phosphorus. I feel $\ce{H3AsO4}$ should be the stronger acid because arsenic atom is larger in size and the charge is spread out in much more volume which should make the conjugate base more stable. What am I missing out?


texts: Carbons have been numbered differently in two different pictures. What are the rules of carbon numbering?


texts: Additive for water to increase the viscosity to a value between 5 and 20 cP

texts: Is there an additive that I can add to water that will increase the viscosity to a value between $5$ and $\pu{20 cP}$? Ideally, I would like the  mixture to be newtonian and since I will be working with gallons of mixture, it would be nice if I didn't have to add too much of the stuff.


texts: I am doing an experiment for a miticide for honey bees. I will be dissolving 600 g of 99.6 % oxalic acid in one liter vegetable glycerin at 150 °F. I have been told it will give off formic acid fumes while mixing and heating. I don't think it will until it get to the melting temperature of oxalic acid. Is there any safety concern? Also what would the shelf life of the mixture be?


texts: Choice of doping elements in semiconductors

texts:
In a typical semiconducting material, we start with silicon (group IV) and introduce atoms of group V or group III depending on whether we are constructing an n- or p-type semiconductor respectively.

Why is it optimal to choose doping atoms one group away? Why not introduce atoms from groups VI or II, for instance?


texts: How do I convert this ion exchange capacity into water softening capacity?

texts:
I am researching for an extended experimental investigation into methods of water softening. One such method is the use of ion exchange resin. I have contacted the supplier of the resin for its exchange capacity, but I'm not sure how their answer relates to the removal of magnesium and calcium ions from water.

They say the exchange capacity is "1.0 mEq/mL min of 99% in H form."


texts: How many stereogenic centres are there in discodermolide?

texts: It is generally said that carbon-carbon double bonds cannot behave as stereogenic centres but the above molecule contains three such centres. Can somebody please point out all the stereogenic centres (including the double bonded carbons) and explain how and why this is so?


texts: Material to change its color by temperature condition meets over time

texts:
There are thermochromic materials which their color changes reversible by temperature. Simply they show their current temperature by color. We can say their color is a function of current temperature:
$$c_t = f(temp_t)$$
Where $c_t$ is color in time $t$ and $temp_t$ is temperature in time $t$

I wonder if there is similar material which their color changes irreversible by history of temperature they meet over time. In comparison to thermochromic material, we can say their color changes by integrations of temperature:
$$c_t = f(\int_0^t temp_x dx)$$
Where $c_t$ is color in time $t$ and $temp_t$ is temperature in time $t$.

This seems to be more general and simpler than thermochromic materials as they are like regular chemical reactions such as oxidation, ... happens every day.

Are there any industry suited solutions out there based on this behaviour which shown in the second equation?


texts: How does one tell (or conclude) if a substance is carcinogenic?

texts:
It's common to read statements like:

  Tetrachloroethene ($\ce{CCl2=CCl2}$) was earlier used as a solvent for  dry cleaning, but since it contaminated ground water and is a suspected carcinogen, it has been replaced by ... .
  Various hydrocarbons harms plant tissues, shed leaves, flowers and twigs. Many of them are also carcinogenic.

How do we tell or suspect one compound to be carcinogenic? And are all carcinogens organic compounds?


texts: Why does the cathode ray tube only start glowing at low pressures?

texts:
I am considering the cathode ray tube of the set up, when the cathode rays were discovered:

Voltage = very high
Gas = any
Atmospheric Pressure = changing

At different pressures, there are different observations:

1 atm: the tube does not glow.
0.1 atm: the whole tube lightens up
0.01 atm: the tube glows at the anode end (Glowing is shown as there is a detector coating of ZnS.)

Note: I don't have this set-up, this is just taken by me from theory.

Why does, when I am just reducing the pressure from 1 atm to 0.01 atm, the tube at first not glow, then it glows completely, and only at low pressure it glows just at one end?


texts: Solid state, closed packed structures, BCC lattice

texts: How many next nearest neighborhood respectively each potassium has in bcc lattice?


texts: Which is more soluble in water and why: K₂HPO₄ or CaHPO₄?

texts: If I dissolve $\ce{K_2HPO_4}$ and $\ce{CaHPO_4}$ in water (two different reactions), the latter shows better solubility. Is it because $\ce{Ca^{2+}}$ has ha higher valence of $2$ than $\ce{K^+}$, which has only $1$? Or has it something to do with the lattice enthalpy?


texts: How does Walter White make pure crystal meth using a non-stereospecific reaction?

texts:
In the fantastic TV series Breaking Bad, Walter White, the dying chemistry teacher, takes to making crystal meth (d-methamphetamine) by several routes.

Initially, he uses the common small-scale route starting with pseudo-ephedrine which uses a stereospecific starring material to make a stereospecific end product (d-methamphetamine is the active compound). But doing this on a large scale is limited because it is hard to get large quantities of the pseudo-ephedrine.

Walter uses his knowledge of chemistry to move to an alternative route starting with phenyl-acetone(or P2P as it often called):

There are several ways of doing the reduction to produce the final product (White first seems to use a Thorium dioxide dehydrocarboxylation in a tube furnace but later seems to favour the aluminium amalgam reduction).

But all the P2P methods produce racemic products. White clearly knows this as the issue of getting the right enantiomer is raised more than once in the show. His product is considered to be exceptionally pure.

So how does he get an enantiomerically pure product? Or perhaps, since the show might not want to tell us the answer, what possible methods could he have used?


texts: How do sugars react with cobalt(II) and ammonia?

texts:
I did an experiment regarding the identification of a range of monosaccharides and disaccharides and wanted to know what the exact purpose of this experiment was and what is was testing.

The following steps were carried out:

Add 10 mL of 5% solution of fructose, glucose and sucrose to separate test tubes.
Add 4mL of cobalt (II) chloride to each test tube.
Heat each test tube to near boiling, then cool.
Add 8 drops of ammonia to each test tube.
Record any colour changes.

Fructose was the only one with an observable colour change.
Why / how does the fructose behave differently from other saccharides? Is it because fructose breaks down in a different way from the other sugars?


texts: NMR chemical shift range of different elements

texts:
A typical $\ce{^1H}$ NMR runs from approximately 0 to 10 ppm, give or take a bit. $\ce{^13C}$ NMR runs from 0 to 200. And $\ce{^59Co}$ NMR runs from -5000 to 15000 ppm!

There seems to be some correlation with atomic number, although three points hardly make a trend. Is there an explanation for this? I'm not interested in the exact numbers, but rather the relative orders of magnitude.


texts: Which compound results in the following products when mixed with AgNO3 and Chlorinated water

texts:
I'm currently working on attempting to identify a particular substance of which I know the cation is Na, however I am unsure as to what the corresponding anion is based off of these characteristics.

The salt is soluble, and when drops of AgNO3 are added to the dissolved substance the liquid turns a dark brown and a nearly black precipitate forms on the top. The liquid remains relatively transparent however. In addition, I observed that when chlorinated water was added to the solution, the solution slowly turns white with a light tint of yellow, like a very light creamy color, it releases some pungent odor however I am not familiar enough with scents to determine whether or not it is an ammonia or sulphur odor. Of the sodium compounds, the following are options:

Sodium bisulfate
Sodium borate
Sodium citrate
Sodium chloride
Sodium fluoride
Sodium nitrate
Sodium nitrite
Sodium oxalate
Sodium sulfate
Sodium sulfite
Sodium thiosulfate

As far as I'm aware the reaction with chlorinated water is just a reaction with Cl


texts:
We have a need for the following types of analysis.  I am not sure what analytical devices would be most suited to the needs.  I'm considering FT-IR and Ion Chromatography.  What do you think?

For the analysis of oil we require the following:

An analytical device to measure TBN total base number.
An analytical device that can measure the additive metals.

For the coolant:

I want to make sure  that in addition to determining chlorides, sulfates, glycolates, nitrates, phosphates, etc.  we also have a requirement to measure Reserve alkalinity under ASTM D 1121.

I look forward to any help you can give.


texts: Calculation of free energy from potential and kinetic energy

texts:
I am having trouble understanding how (and even whether it's possible) to get free energy from kinetic and potential energy.
I have run molecular dynamics simulations (NPT ensemble, CP2K software), but this is a basic thermodynamics question.  There's a results file called "energy."  The file contains energy-related output: temperature, kinetic and potential energy, and a "conserved" quantity.
(The "conserved quantity" is the sum of the kinetic and potential energies and also the thermostat energies).
From courses a long time ago and reading I have done online, I know that
kinetic energy + potential energy = total energy

I think "total energy" would be the internal energy.  It would be great if someone could please confirm/debunk that--I don't know if the situation is distinct for distinct ensembles, for example.  Whatever the case, I don't know how it relates to the free energy.  I would like to know if I have enough information to calculate the free energy.
If anyone could please point me in the right direction, I would appreciate it.  I can't find anything online and maybe that's because I don't even know where to start looking.


texts: Availabilty of magnesium ions in phosphate buffer

texts:
Phosphate buffer is a common buffer in biological applications, it's especially popular for NMR. Magnesium ions are necessary for many biological systems to work, though the amount of magnesium ions you can add in a phosphate buffer is limited by the relatively low solubility of magnesium phosphate.

What I'm curious about is whether the phosphate buffer can affect the availability of magnesium ions even in concentrations where no visible precipitation occurs? Common phosphate buffer concentrations are around 10-100 mM, and magnesium ions are usually 5 mM or below. At those concentrations I see no visible precipitation, but is the magnesium actually fully available or is the phosphate sequestering it and thereby lowering the effective magnesium ion concentration in the solution?

Even just calculating the solubility of magnesium salts in phosphate buffer is not straightforward, as there are multiple species of magnesium phosphate and possibly even other salts like $\ce{MgKPO4}$.

Does phosphate buffer affect the availability of magnesium ions in solution compared to a non-interacting buffer? If that is so, is there a way to calculate the size of that effect?


texts: Deviation from Raoult's law because of adhesive and cohesive forces

texts:
A solution made of two or more compounds have adhesive and cohesive forces. Cohesive forces are the attractive forces between the same molecules. Adhesive forces are the attractive forces between different molecules of the solution.

A real solution shows positive deviation from Raoult's law when the cohesive forces are stronger then adhesive forces. It shows negative deviation when the adhesive forces are stronger than cohesive forces.

Why do stronger cohesive forces in real solution make positive deviation and stronger adhesive forces make negative deviation from an ideal solution?


texts: If there is a ketone and ester functional group in the same compound and I want to protonate with $\ce{HCl}$, which one will protonate first? Is it the carbonyl group in the ketone or the carbonyl group in the ester and why? Is it related to the $\mathrm{p}K_\mathrm{a}$ of the functional group?


texts: How to use Lewis theory to differentiate between an acid and a base?

texts:
According to Lewis theory a material is an acid if it accepts an electron pair, and a material is base if it donates an electron pair. But if we compare the structures of $\ce{HNO3}$ and $\ce{NaOH}$, i.e.

$$
\ce{H-\underset{.\!.}{\overset{.\!.}{O}}-\underset{\underset{\huge :O:}{||}}{\overset{+}{N}}-\underset{.\!.}{\overset{.\!.}{O}^}\!:^-}
\quad
\text{and}
\quad
\ce{[Na]+ [:\!\underset{.\!.}{\overset{.\!.}{O}}H]-}
$$

there are so many lone pair of electrons which can be shared, and in both structures there is a positive atom, so they can accept a lone pair. How can I say that one of them is acid and the other one is a base?


texts:
Give me a hint to solve this question,

what should my first step ?

should convert the grams into moles ?

aluminum= (54g/150g)= 36% ( percent composition of aluminum)
sulphur= 64%

0.36x=20 (36 percentage of what is 20)

x=20/0.36
x=55.5 grams

is there a more easy way ? to do in mind


texts:
Is an SN1 reaction possible in halobenzene?

Will the phenyl carbocation be stabilized via resonance? Suppose the leaving group is very electronegative and the environment is protic. What then would be a suitable nucleophile?


texts:
What does activated carbon do to gasoline vapor? After the vapor is absorbed into a charcoal EVAP canister, what is left to be sent to the engine?

My question is in reference to the work of Tom Ogle and the carburetor he made in the 1970's, and I just want to find out if his invention is plausible.

Fuel enters the ignition chamber while still in its liquid form.
http://fuel-efficient-vehicles.org/energy-news/?page_id=787
I want to know if this is possible


texts: I was given the problem to arrange all cyclic isomers of $\ce{C6H12}$ from the lowest to the highest heat of combustion. I found twelve isomers and quickly realised that cyclohexane is the most stable and thus has the lowest heat of combustion, since it has zero strain, and that the only cyclopentane isomer - methylcyclopentane, follows after since it does not have much strain. However, what confuses me is the stability of the other isomers (four cyclobutanes as well as six cyclopropanes). I understand that the cyclobutanes are more stable than the cyclopropanes, but what about the substituents? How do they affect stability?


texts: Why doesn't anyone manufacture 4.5 V cells?

texts:
Every 4.5 V lantern batteries are a series of three 1.5 V cells. It would have more capacity if it consisted of single 4.5 V cell. But I don't see any 4.5 V cell.

According to Wikipedia's Standard Electrode Potential data page, there are vast possibilities of a 4.5 V cell. The one I think most plausible is:

$$
\begin{align}
\text{Anode:} &\quad &\ce{Ca + 2 H2O &→ Ca(OH)2 + 2 H+ + 2 e-} \quad|\cdot 5\\
\text{Cathode:} &\quad &\ce{2 BrO3- + 12 H+ + 10 e- &→ Br2 + 6 H2O}\\
\hline
\text{Overall:} &\quad &\ce{5 Ca + 2 HBrO3 + 4 H2O &→ 5 Ca(OH)2 + Br2}
\end{align}
$$

Have anyone tried this or anything else 4.5 V?


texts:
I was reading Introduction to quantum mechanics by David J. Griffiths and came across following paragraph:

" 3. The eigenvectors of a hermitian transformation span the space.

As we have seen, this is equivalent to the statement that any hermitian matrix can be diagonalized. This rather technical fact is, in a sense, the mathematical support on which much of a quantum mechanics leans. It turns out to be a thinner reed then one might have hoped, because the proof does not carry over to infinite-dimensional spaces."

My thoughts:

If much of a quantum mechanics leans on it, but the proof does not carry over to infinite-dimensional spaces, then hermitian transformations with infinite dimensionality are spurious.

But there is infinite set of separable solutions for e.g. particle in a box. So Hamiltionan for that system has spectrum with infinite number of eigenvectors and is of infinite dimensionality.

If we can't prove that this infinite set of eigenvectors span the space then how can we use completness all the time?

Am I missing something here? Any missconceptions?

I'd appriciate any help.


texts: According to the image above (source), for a radius-ratio between 0.732 and 1, the coordination number is 8. However, for a radius-ratio of 1, the coordination is 12. This is the same for the boundary values between the other coordination numbers, but I’m focusing on the radius-ratio of 1 for now. I don’t understand how the same boundary value could correspond to two different coordination numbers. If you have a monoatomic metal, then all the atoms constituting it have the same radius and the radius-ratio is 1. In order to achieve the closest packing possible, the metal atoms would form a CCP or HCP structure, wouldn’t they? Those two crystal structures have the greatest coordination number. Yet other monoatomic metals, with a radius-ratio of 1, form can BCC structures, with a coordination number of 8. Why would they form such a structure when their radius-ratio can also correspond to a CN of 12? How can one radius-ratio correspond to two CNs?


texts: What property allows ozone to absorb uv light

texts: Why can ozone act as a barrier of UV light, so that we don't get irradiated by the sun's energy, and not any old molecule? In a recent exam I sat, one of the questions was "Name one physical property of ozone and contrast it with oxygen" and under exam pressure I spurted this onto the page: "Because the coordinate covalent bond in ozone is weaker than a traditional covalent bond, the bond is free to 'wiggle' about a bit. This means that the ozone can absorb a range of frequencies of photons, as a completely rigid molecule like oxygen would only have very specific frequencies which it could absorb." How much of this 'guess' is grounded in fact, or in other words, what is the actual mechanism that allows ozone to protect us from UV rays and not any old molecule?


texts: Is it possible to self-teach yourself most of organic chemistry and biochemistry without access to a lab or university resources?

texts:
I'm stationed on a US Navy warship and I often wonder if its possible to master these subjects without access to a college instructor. I've been reading introductory books on organic chemistry and while I've gained a lot of knowledge over the past year, I still cannot carry out any experiments.

I have three more years left on my contract before I can ever step foot in a chemistry classroom. I would like to eventually know everything about organic chemistry and biochemistry from reading IR spectroscopy / NMR signals to knowing everything about the properties of various functional groups along with their medicinal applications. I would like to get to the stage where I can propose what reagents to use for various reactions, but I realize that is made more difficult by the fact that I don't have direct experience in the lab.


texts: How does a limiting reactant relate to the concentration of ions in solution?

texts:
Given the question

  A sample of $\pu{1.50 g}$ of lead(II) nitrate is mixed with $\pu{125 mL}$ of $\pu{0.100 M}$ sodium sulfate solution. What is the limiting reactant in the reaction? Calculate the concentrations of all ions that remain in the solution after reaction.

I first found the chemical equation for this problem to be:

$$
\ce{Pb(NO3)2 (aq) + Na2SO4 (aq) -> PbSO4 (s) + 2NaNO3 (aq)}
$$

I found the limiting reactant to be $\ce{Pb(NO3)2}$ because there are fewer moles of that substance than the $\ce{Na2SO4}$, with there being  $0.00453 \,\mathrm{mol}\, \ce{Pb(NO3)2}$.

I then used the limiting reactant to find the concentration of each ion. I multiplied 0.00453 mol by the number of moles of each ion in the equation, and put that over 0.125 L to get the molarity. However, the correct answers are

  no $\ce{Pb^{2+}}$ ions are left in solution
  $[\ce{SO4^{2-}}] = 0.0638 \,\mathrm{M}$
  $[\ce{Na^+}] = 0.200 \,\mathrm{M}$
  $[\ce{NO3^-}] = 0.0725 \,\mathrm{M}$

I only got the concentration of $\ce{NO3^-}$ correct. What have I done wrong? I think my mistake has something to do with using the limiting reactant in the equation. Also, I understand why there is no $\ce{Pb^{2+}}$ in the solution, because it is in solid form, but doesn't that mean the $\ce{SO4^{2-}}$ should also produce no ions since it is bonded to the $\ce{Pb^{2+}}$?


texts:
Based on the Lewis structure of arginine, the terminal primary amine attached to the guanidine group seems to be $\mathrm{sp^3}$ hybridized and trigonal pyramidal. Also, in quantum mechanical computations, it is shown  that all carbon-nitrogen bonds in the guanidine group are different lengths.

However, in the 3d structure below, the entire guanidine group is planar, indicating an sp2 hybridization. Why is $\ce{N}$ $\mathrm{sp^2}$ and not $\mathrm{sp^3}$ hybridized? Why is the guanidine group planar? Why are all the bond lengths different if all the $\ce{N}$ atoms are $\mathrm{sp^2}$?


texts: if I have concentrated acetic acid (99%) what are the out put gases during electrolysis?

texts:
If I use concentrated acetic acid (glacial acetic acid($\ce{CH3COOH}$)) as an electrolyte. What ions are produced at the anode and cathode?
Can I get ethanol with it ($\ce{C2H6O}$)? If not, what would be the products?


texts: Spectrophotometry: shifting absorbance curves vertically so isosbestic points match

texts:
We're measuring reaction kinetic parameters of a hydration reaction (Co complex) by measuring the absorption spectrum a different time intervals, and calculating the ratio of product to reactant by comparing the absorbance measured to the absorbance spectrums of the product and reactant in pure form. Water baths at 6 different temperatures were tested and for certain graphs, the results are coherent, with curves meeting around the isosbestic point (where the absorbance of both product and reactant are the same, first graph). However for certain graphs there is a significant vertical shift on certain curves which renders the results incoherent (second graph)

I had the idea to shift the stray curves down to match the isosbestic points of the product and reactant, as this should technically be constant whatever the reaction progression (at a given concentration). I realize this will render the use of the Beer-Lambert law pointless as we are completely fabricating our results, however what is important is the ratio of product and reactant, relative to other curves, which will be conserved, and these will actually be comparable once the isosbestic points match.

I just wanted some outside input

-Is this unscientific? Will my TA wonder what the hell i've done and take points off, or is this process justifiable

-Should i just process and present my data without trying to correct the error.

-What could this baseline error be caused by? since the errored curves seem to be shifted up, i'm suspecting condensation on the cuvette walls increased the absorbance, as the water baths went up to 50 degree. Although I dont remember noticing condensation on the cuvettes.

Thank you for any input.


texts: What is an easy way to reduce a boronic acid to borane?

texts:
I have a selection of boronic acids that I want to reduce to borane forms. Some of the boronic acids in question are phenylboronic acid (C6H5B(OH)2), tolylboronic acid (C7H7B(OH)2), and p-phenylenediborinic acid (C6H4(B(OH)2)2). I want to convert them into phenylborane (C6H5BH2), tolylborane (C7H7BH2), and p-phenylenediborane (C6H4(BH2)2).

I think I can do this by dissolving the boronic acid in ether and adding Lithium Aluminum Hydride (LAH). Giving a reaction that looks something like:

However, I am afraid that, given how aggressive a reducing agent LAH is I might get something like:

So I guess I have two questions:

Will LAH attack the boron-carbon bond shown in the second reaction diagram?
Can the reduction of the boronic acid be accomplished via a less aggressive reducing agent, perhaps Sodium BoroHydride?

Just a note: I am well aware that the boranes produced will be oxygen sensitive, either converting back to boric acid on exposure to oxygen, or catching fire.