texts: Can the experimental mole fraction equal one?

texts:
I recently did an experiment on the temperature dependence of phase equilibrium acetone $\ce{C3H6O_{(l)}} \to \ce{C3H6O_{(g)}}$ I'm at the stage where I need to find the experimental mole fraction $\chi_e$ which I did by plotting a graph (see below)

From this graph I can simply find $\chi_e$ by finding the slope. I took two points $(56,50)$ and $(66,60)$ and found $$\chi_e = 1$$

This doesn't look right to me, so I'm just asking if someone can let me know if what I've calculated is correct or way off the mark

EDIT: I just calculated the theoretical mole fraction there and got $$\chi_T = 0.94$$

The moles of the non-volatile solute and pure acetone were known.


texts: Why does ClO₄⁻ only have 3 double bonds?

texts:
It seems that most people draw $\ce{ClO4^{-}}$ with three double bonds and the negative charge on the oxygen:
http://www.chemspider.com/Chemical-Structure.109953.html

However, it would seem that it is more stable for the negative charge to be on the chlorine as it is more electronegative? (thus giving 4 double bonds to each oxygen)


texts: Why highly unstable cyclic boron compounds should be stabilised by two electron reduction?

texts:
I am trying to figure out why highly unstable cyclic boron compounds  could be stabilised by two electron reduction...

My thoughts are because each Boron has an empty p-orbital perpendicular to plane of cyclic compound, pi-orbitals can form like diagrams below.

The two electrons would then go into the pi-bonding orbital, thus stabilising the entire compound.

Is this the correct explanation? If so, how can vibrational spectroscopy be useful in examining the bonding in the dianion?


texts: How does Melatonin put you to sleep? How is this compound radio-protective?

texts:
Melatonin (IUPAC semi-formal name: N-acetyl-5-methoxytryptamine) is a hormone produced in humans, animals and some of plants. It's mainly famous for being the drug suggested to people with sleeping problems, jet lags and even insomnia (in trivial cases, still experimental). Recent studies have shown this compound's role as an anti-oxidant and a protection for mitochondrial DNA.
Melatonin interacts with the immune system; and is clinically proved to have anti-inflammatory effects. It can act as a radio-protective agent...
Hold it there. This is chemistry, not biology. First of all, how is Melatonin radio-protective? And what is in that structure that makes it radio-protective? 2nd, what reactions occur in the body, in presence of Melatonin, that cause sleepiness (resources have claimed the chemical function to be a mystery but I doubt that's true)?
 Most of the info above is available at the wikipedia: Melatonin.image credit: http://cenblog.org/the-haystack/files/2011/06/melatonin.png


texts: Is it possible to blow out a candle flame using pure oxygen?

texts: This sounds like a stupid question perhaps, but if a stream of pure $\ce{O2}$ was directed at the flame as a concentrated jet would it blow off the candle?


texts: Why H2O2's molecular geometry is what it is...?

texts:
I came up with this question when I was trying to determine whether H2O2 is polar or not.

H2O2 looks like this when looked parallel to oxygen-oxygen bound:(source: Pubchem)

Each hydrogen is in one of the three positions available around each oxygen(the two nonbonding electron pairs occupy the other two); even the oxygen-oxygen bound can rotate to set hydrogens in any position relative to each other.  Therefore I don't see the problem in following nonpolar structure(pretty neat!)

What concept am I missing while determining molecular geometry?

Is a H2O2 molecule sometimes polar and sometimes nonpolar?

Thanks for your help!


texts: Reasons for antiperiplanar arrangement in E2 reactions

texts:
From what I have learnt, there are 2 reasons that synperiplanar arrangement cannot give E2 reactions:

In Newman projection, synperiplanar arrangements is in a eclipsed form (very high in energy), so less likely to be in syn formation than anti. However, I am thinking that as the C-C sigma bond is always rotating, there is still a little chance for synperiplanar to undergo E2

In synperiplanar arrangement, the base (usually rich in electron density) will face a high electron repulsion with the leaving group when approaching the beta-hydrogen, hence reduce chance of successful E2.

However, these reasons only reduce the chance of synperiplanar arrangement from going E2, but cannot comepletely eliminating it. So I want to ask whether there are other reasons (e.g. cannot form / break the bonds if in synperiplanar during E2), in line with the experimental results that only anti can gives E2?


texts:
I have a furiously overwhelming question-

  Why is the atomic size of noble gases larger than the atomic size of
  the previous halogen  when atomic sizes decrease across a group?

I did search it on the net and asked my teacher but everyone says that because noble gases are usually not bonded.

But:

Why does being "bonded" decrease atomic size?

Also we are talking about the atomic sizes of isolated elements?


texts:
At the moment I'm writing a paper about sweeteners and want to compare saccharides, polyoles and synthetic sweeteners like cyclamate.

I'm having some problems trying to apply the Shallenberger–Acree model and would like an explanation for Glucose/Sucrose and Maltitol since I already figured it out for Cyclamate.

Please keep your English simple since it isn't my native language.


texts: Why is there an upper limit to the photon energy that can be observed in the discrete emission spectrum of the hydrogen atom?

texts: I think it must have to do with the fact that an incident photon with a sufficiently high energy will ionize the hydrogen atom (i.e. the electron will be ejected). Therefore it won't show in the emission spectrum. Is this correct?


texts: Concentration of dissolved lead(II) bromide

texts:
Calculate the concentration of $\ce{Pb^2+}$ and $\ce{Br-}$ when $\ce{PbBr2}$ dissolves in water. $K = 7.9 \times 10^{-5}$

$$\ce{PbBr2 <=> Pb^2+ + 2Br-}$$

In most cases we have the concentration of the solute, but here we don’t. How should I be thinking now?

if it’s $1~\mathrm{M}$ for example

$$K = \frac{[x][x]^2}{[1-x]}$$


texts: Why can't a reverse fission reaction be automatically classified as a nuclear fusion reaction?

texts:
$$\ce{_2^4He + _13^27Al -> _15^30P + _0^1n}$$

Will this reaction qualify as a nuclear fusion reaction? The answer to this question in the test says that it won't, yet it seems to be the reverse of a fission reaction.
Why would it not be considered fusion?


texts:
Today I finally mustered the courage to go and talk to the director of the labs to politely ask him if I could use the labs out of class hours. Long story short, our lab sessions "are bad" because we are given a protocol, and like babies we just need to follow it. No brainer, and I am against that. So I got permission to use the lab for experiments that don't pose a mayor risk, as well as a slight restriction of the reagents.

I'm not sure of which reagents we have in the lab, but there aren't that many there. So, now to the point. I was hoping that you could tell me which experiments I should try. I came up with the idea when we worked with ferric ammonia ferrocyanide $[Fe(CN)_6][Fe(NH_4)_2]$ and I had to balance the chemical equation of the reaction that we used. However, I had no idea of what the byproducts where, because I had no way to test for their presence! My idea is to bring an hypothesis and then, starting pretty much from scratch (except reference tables or such) prove or disprove it.

Could you share a nice example of something I could test in the lab? If not, where can I find stuff that I can work with, without getting the answer right out of where I got the info. Did I get to express my idea correctly? More or less?

Thanks for the help!

P.s.: I kindly asked a professor to supervise my work, so I would get help regarding methodology.


texts: Determine the molecular formula of the compound using percentage composition

texts:
I’ve attempted to solve this problem with percent composition, but it says the answer is wrong. Is it a $pV=nRT$ problem, and if so, can I use the units as they are given?

  A $\pu{0.02867 g}$ sample of gas occupies $\pu{10.0 ml}$ at $\pu{290.0 K}$ and $\pu{1.10 atm}$. Upon further analysis, the compound is found to be $38.734 \%~ \ce{C}$ and $61.266\%~\ce{F}$. What is the molecular formula of the compound?

I keep on getting $\ce{CF}$ for the answer via percent composition.


texts: Why do steel and iron not passivate the way aluminum does?

texts:
When aluminum is exposed to oxygen a micro layer or film of oxide appears on the surface and oxygen cannot penetrate any further.

With iron or steel, however, oxygen continues to reach into the metal, rusting it deeper over time. When iron is heated the oxide ("scale") forms much faster and the oxygen can deeply penetrate into the metal.

What is the reason that aluminum and iron are different in this way?


texts: Copper layer doesn't stick after Copper electroplating

texts:
I am playing around with copper plating using Copper Sulfate solution with electricity.
I am using 2-2.5 volts as power source and around 100-500 mA.
It is actually a very small container around 100 ml of the solution.

I have used copper sulfate anhydrous to make the solution and I have mixed around 20 mg with around 200ml of tap water in normal room temp.

I have tried several materials (iron, copper , steel, graphite) but I end up with a layer of copper that can be easily removed, even I leave it for fair amount of time(up to 15 min), the result layer is actually is not thin at all but still can be easily removed!!

What is the thing that I am missing here, I have seen people doing this on the internet for just like 5 min. and the layer that they create seems very strong!!


texts: Why are peroxides unstable but disulfide bridges considered stable? Why are esters stable but thiolesters are unstable?

texts:
I can not understand why a peroxide $\ce{R-O-O-R}$ is considered reactive and unstable.

Going down one row on the periodic table, a disulfide bridge ($\ce{R-S-S-R}$) is apparently super stable and super important to proteins 3d structure.

At the same time, a thioester is considered to be as unstable/reactive as ATP and the ester is the stable one?

What am I conceptually missing here to explain this contradiction?


texts: Why are group 1 elements called alkali metals and group 2 elements are called alkaline earth metals?

texts:
I was studying the periodic table. My teacher said that

  Group 1 elements are called alkali metals because their oxides are soluble in water and group 2 elements are called alkaline earth metals as their oxides form in the earth and are water soluble.

What did she mean by "oxides"? Aren't alkali metals bases which are soluble in water? Then what is the term "oxides" doing here?
What is the difference between "alkali" and "alkaline"? Why do we call one of them "alkali metals" and the other "alkaline earth metals" when the concept is the same?
Why are the bases of group 1 and group 2 elements soluble in water? What is the reason?


texts: How much carbonation is in one liter of commercial fountain Coca-Cola

texts:
From what I understand generally Coke is carbonated to roughly 6.2 g per liter in bottles and cans, or 3.1 volumes of CO2.  I was watching this video because I was curious about how fountain soda machines worked.

https://www.youtube.com/watch?v=RRHNt67xbMs

By the end of the video they suggest that the soda is carbonated to around 5 volumes of carbonation.  Which as I understand would be somewhere in the realm of 11 g of CO2 per liter, almost twice that of the normal soda.  I imagine there are a couple other factors involved, like they are dispensing more CO2 than is actually dissolved in the soda as a consequence of trying to instantly carbonate.  According to everything I know about carbonation I know from beer making they are carbonating almost 20 times higher than a forced beer carbonation technique in home brewing.  Can anyone help me better understand this?  I would think that the carbonation level difference between bottled and fountain soda would be something highly controlled by beverage companies for the sake of product consistency.

I did some additional reading and found that the correct maintenance levels on soda fountains with chilled water to roughly 40 degrees F is 75 psi if that helps.  For 3.1 volumes of carbonation as I understand equilibrium would be just like 5 psig.  I know I missing something big.

I can only assume that the rate of carbonation loss is inversely exponential as the carbonation approaches closer to equilibrium for the environmental pressure.  Would 5 volumes rapidly decarbonate to 2-3 volumes but not get much lower very quickly?


texts:
I use a solar still that holds 182 cubic feet of water. Here is how it works:

There is an insulator on both sides of the metal bowl. On the outside it covers the whole thing. on the inside it covers the sides but not the bottom. This collects the rain and also heats up the rainwater during sunny days so that the evaporation rate is faster. I have the pipe nearest the metal bowl the largest it can be while the metal bowl still collects rain and gets heated up by the sun. The water and any gases pass through there and into the condenser. I have this cold enough to condense water into a liquid but not so cold that the water turns solid and the $\ce{CO2}$, $\ce{O2}$, $\ce{N2}$ etc. turn liquid. Last but not least there is a spigot at the very end and a bucket below it. This separates atmospheric gases from liquid water with $\ce{CO2}$ being the main concern.

There is also dust and pathogens from the air in rainwater.

The dust most likely will stay behind and just make the bowl dusty. The pathogens get killed by the heat that there still is when all the water has been evaporated.

I would say the maximum loss with this system is from 1 pint or so to 1 gallon or maybe more depending on the water level in the bowl.

However I think there is a way to calculate maximum and minimum loss(neither of these is 0).

How could I calculate maximum and minimum loss based on the depth of the water(because obviously at different depths there is a different amount of loss) and the size of everything(which by the way the pipe slowly tapers off to a certain size and so you have to take pressure into account as well as volume)?

Also how could I calculate the pressure in the pipe based on the fact that it tapers off and starts at the maximum size possible with the bowl still collecting rain and being heated by the sun?


texts: Crystal field splitting in complexes other than octahedral or tetrahedral

texts:
Is there a methodology to developing the crystal field splitting diagram for various crystal fields?  I know the octahedral and tetrahedral diagrams, but if I'm asked to draw something like square pyramidal, trigonal prismatic, etc. that I haven't memorized, then is there a process I can go through?  I searched Google, but am having little luck finding anything that shows the process.

Thank you!


texts:
In the formation of 3-bromo-1-butene and 1-bromo-1-butene, from $\ce{HBr}$ and $\ce{C_4H_6}$, in a gas phase:

$\ce{HBr + C_4H_6 \to 1BrC_4H_7}$

$\ce{HBr + C_4H_6 \to 3BrC_4H_7}$

the number of degrees of freedom is given by: $F=C-P+2$

I'm trying to rationalise this but finding it quite confusing. For example, can we state that there is only 1 phase, i.e. a gas phase?

And the components, is the isomer of one independent of another? I'm taking there to be 3 individual components.

My answer is then 4 degrees of freedom, which seems okay, given $p$, $t$, $X$, $V$ could vary?

I'd appreciate your help in this, thanks.


texts: Does using stonger soaps help me lose weight?

texts:
Soaps are amphiphilic molecules that, practically, removes body oils from the surface of the skin. The body, on the other hand, always replenishes sebum through the sebaceous glands after a certain amount of time.

Applying Le Chatelier's principle to this complex chemical equilibrium, where the equilibrium shifts towards the right hand side, where oil is being extracted from the equation, essentially so:

(body · oil)  ⇌  body + oil       # RHS preferred

Because the process of sebum regeneration must be endothermic, this means the body is losing energy in this overall process:

body + (lipids + heat)  ⇌  body + oil  ⇌  (body · oil)

My questions are:

Are my assumptions correct?
Does removing oil from the body more readily, by means of a stronger detergent/soap, reduce body mass?
Does the temperature of the water bath used in the experiment affect the rate of sebum dissociation?


texts: How does the electron configuration correlate with the emission spectrum of an ionic compound?

texts: trying to find a way to correlate the electron configuration of an ionic compound (ie. Cupric sulfate, potassium chloride, Cupric chloride, sodium carbonate, strontium chloride) with its emission spectra.


texts: Would graphene be a good efficient conductor of electricity in mobile phones

texts:
Gold is commonly used in mobile phones as an electrical conductor,as it is apparently better than copper at conducting electricity
Quoting from extremetech.com :

"The materials recovered are reused in new electronics parts and the gold and other precious metals are melted down and sold as ingots to jewelers and investors as well as back to manufacturers who use gold in the circuit boards of mobile phones because gold conducts electricity even better than copper."

(Some of the information is irrelevant but i was to lazy to take it out)

But when I actually look at this table it says that gold is worse than copper at conducting electricity and has a higher resistivity rate

Please follow the link to see what I'm talking about
Table of conductivity

So it's either that the information on the table is wrong or that the tech website was wrong (and it probably was)

Information found on investorintel.com

"Graphene is fantastically good at conducting electricity; its current density is 1,000,000 times greater than copper’s and its intrinsic mobility is 100 times greater than that of silicon. Electrons move through graphene with virtually no resistance and without mass. This means that graphene can carry electricity more efficiently, precisely and faster than any other material. It is anticipated that graphene will enable lithium batteries to have more than 10 times the electrical retention/capacity as anything presently in use."

But there are problems of it being to expensive to manufacture, but I do not understand why?

To clarify what I'm asking
1. Is gold better at conducting than copper
2. Is graphene better and more efficient at conducting energy (thermal and electrical) than any other known elements?


texts: Single Crystalline Thin Films is detect by GIXRD?

texts:
I understand epitaxal thin film, have lattice match with substrate.
But what about those films that doesnt match but have only one XRD peak? Is this proof of single crystale thin film?


texts:
Potassium ($\ce{K}$) seems to be the transitional alkali metal in terms of safety. Lighter than $\ce{K}$ and we can store under oil with no worries. Heavier than $\ce{K}$ and only ampules will work. $\ce{K}$ is such that even under oil it can absorb enough oxygen to form superoxides that are contact explosives. But this is the theory: does anyone have any experience with extended proper storage of potassium?

I ask for two reasons. First, there are lots of online videos showing $\ce{K}$ under oil that the scientist then proceeds to cut, smash, and otherwise manhandle with no fear of detonation. Second, my $\ce{K}$ arrived tarnished, which I have stored under oil, and then vacuumed sealed in a bag, which has shown zero change in visual oxidation. So while I get that leaving an open jar of $\ce{K}$ under oil is problematic, I'm less clear on well stored $\ce{K}$.

So I'd appreciate any comments from practitioners that use $\ce{K}$ regularly. What situations are genuine dangers? Thanks!


texts: How can I figure out which coupling constants match which hydrogen?

texts:
I am looking for some guidance assigning the $J$ coupling constants to the corresponding hydrogens. Here is my data:

I can obviously see that shift 3.56 is for the methyl group. I can also see that the 4.63 is for the hydrogen adjacent to the methoxy group as it can only couple ($J=\pu{0.8Hz}$) to one hydrogen next to it. Is the approach then to see that the hydrogen at shift 4.04 also has $J=\pu{0.8Hz}$ so this must be adjacent (going clockwise from C of methoxy, next C along)?


texts: ¹H NMR and MS analysis of products obtained by Claisen condensation reaction between methyl 2‐methylpropanoate and sodium methoxide

texts:
A student attempted to perform the Claisen condensation below and  analyzed their isolated product by 1H NMR and MS.
Propose structures for  both the expected Claisen product and the observed product of this  reaction.
What could the student change to obtain their desired product?

This question was asking me to predict the product, both expected and observed.


texts: How many different alkyl chlorides result from C4H10 and chlorine?

texts:
Let's say there's a reaction $\ce{C4H10 + Cl2}$ taking place under UV light. How many different alkyl chlorides do we obtain?

I'm not sure if the resulting molecule would be monochlorinated or dichlorinated? My guess was monochlorinated, as $\ce{HCl}$ is also going to be a product. And I assumed there would be 2 different alkyl chlorides as there are two different possibilities for a chlorine to be attached to a carbon of a butane.  But I guess I was wrong as the answer the book gives is 4 and not 2. How can the book’s answer be rationalised?


texts: Dependance of heat capacity at constant volume on temperature for solids and liquids

texts:
In thermodynamics we have an equation for the change in internal energy:
$$\mathrm dU = nC_V\,\mathrm dT\tag{1}$$
$$\int{\mathrm dU} = \int{nC_V\,\mathrm dT}\tag{2}$$
Since $C_V$ is independent of temperature, for an ideal gas
$$ΔU = nC_VΔT\tag{3}$$
Why is $C_V$ independent of temperature for an ideal gas? On the other hand, in case of solids and liquids, $C_V$ may or may not depend on temperature. Why?


texts: Why do aqueous solutions always have to be electrically neutral?

texts:
I was reviewing some analytical chemistry and stumbled upon a section that explained the imperfection of using a salt bridge.

It said that the using dissimilar ions is a problem because in, for example, the case of KCl the K+ and Cl- have different mobility and so you get regions that are rich in K+ and others rich in Cl-. This means that some specific parts of solution (even though it's small) to be not electrically neutral i.e. electrically charged.

So I imagine in theory at least it must be possible to somehow extract these charge-rich areas and put them into a beaker. So what is all this I've been learning about solutions having to be electrically neutral?


texts: In an experiment testing catalyst influence on reaction, is NaOH a reactant or a catalyst?

texts:
I have recently completed an experiment with hydrogen peroxide (5%), 0.1M KI and 1M NaOH.

Is the sodium hydroxide a reactant or a catalyst in this experiment?


texts: Why does 2-pyridone with chlorine gives 3,5-dichloro-2-pyridone?

texts: Why does 2-pyridone react with chlorine to give 3,5-dichloro-2-pyridone? I thought that 2-pyridone is resistant and will yield only 5-chloro-2-pyridone or even a combination with 3-chloro-2-pyridone


texts:
There is a SMARTS pattern that was published which looks like the following[1]

[#6 × 4]

and there are actually spaces around the × symbols between the 6 and 4.

Question is, should I change this multiplication notation to a lower case "x", or really use some sort of ASCII symbol?  I didn't see a multiplication symbol anywhere in the Daylight SMARTS description.

References:

Hou, T. J.; Xia, K.; Zhang, W.; Xu, X. J. ADME Evaluation in Drug Discovery. 4. Prediction of Aqueous Solubility Based on Atom Contribution Approach. J. Chem. Inf. Comput. Sci. 2004, 44 (1), 266–275. PDF


texts: In High Performance Liquid Chromatography, why are ratios of solvents used?

texts: How do they allow for better separation? For example, why isn't 100% hexane used?


texts: Name for a spin state with a multiplicity of 13

texts:
If I want to name a spin state with 12 unpaired electrons,
what is the correct name?
Tredecim is the latin name for thirteen, but tredecimet sounds odd.


texts: Lowering energy in molecular orbital mixing

texts:
When drawing molecular orbital diagrams for mixing two orbitals we always end up with one orbital which is lower in energy than the initial orbitals and another which is higher in energy. The principle extends to mixing of more than two orbitals with the total number of orbitals always being conserved.
Often we will use arguments involving mixing of molecular orbitals to form MOs of a slightly lower energy to explain phenomena such as hyperconjugation with diagrams such as this.

In this situation, when you have one filled and one empty orbital, the electrons always end up in a lower energy than they started.
What stops you from mixing these orbitals again to produce even lower energy orbitals, even if the energy difference is very small? I understand that symmetry might have something to do with it but I am not well versed in the more mathematical elements of MO theory such as symmetry groups. Or is my initial assumption that mixing two orbitals always results in a lower energy wrong?


texts: Temperature as an independent variable in an endothermic reaction

texts:
My experiment involves the reaction between sodium bicarbonate and acetic acid. I'll be changing the temperature between each trial and measuring the change in pressure by the gas produced. From here I hope to determine the rate expression, rate constant, activation energy then finally produce an Arrhenius plot.

My question is since this reaction is endothermic, how do I account for the change in temperature as the reaction proceeds? I also can't seem to find any published literature value for this reaction's activation energy or enthalpy change, and would love it if someone pointed out a database or something similar.


texts:
Exothermic reactions are essentially reactions that release energy as heat (in part, at least) to the surroundings, and may cause an explosion or combustion, depending on the amount of heat released and the specific conditions (see this story as an example of an unexpected exothermic reaction at home).

We mix up all kinds of stuff at home, mostly in the kitchen, and each "ingredient" may be composed of numerous distinct chemical compounds. This huge number of possible combinations might make it probable that a redox reaction, which may be exothermic and there's no telling how much exothermic, will happen from time to time when mixing two (or more) foodstuffs together. However, it is pretty rare to hear about significant exothermic reactions that may be called "a household accident", such as the one I brought earlier.

My question is: how is this so? Is there any energy threshold that we do not normally cross in the kitchen? Or are the concentrations not large enough? How come kitchen chemistry is not more violent than it actually is? What makes "experimental" food chemistry safe for billions of people without chemistry knowledge?


texts: What is the anodic reaction of aluminum in water

texts:
Standard electrode potentials are reported for materials that are not usable as actual electrodes in water because they react spontaneously and rapidly. https://www.engineeringtoolbox.com/electrode-potential-d_482.html
Some metals, like zinc, are useful as cell electrodes if pure, but if not so pure, exhibit cathodic areas that cause the metal to corrode and produce hydrogen without delivering useful external current. One way to counteract that was to coat the surface with a tiny bit of mercury, which apparently coated the cathodic sites but permitted the zinc to migrate thru as if the mercury were not there.
Other metals, like aluminum, develop a film which inhibits corrosion by developing a resistance to atom/ion movement. It has been suggested to me that the actual electrode reaction on aluminum in water is production of hydrogen, so that the half-cell using an aluminum electrode in water is the hydrogen electrode, because bare aluminum reacts immediately with water. This would be analogous to the zinc anode with surface impurities (cathodic sites), except that we do not consider zinc to be producing a hydrogen electrode, just corroding.
it seems that there is considerable usage of metals like zinc, aluminum and magnesium for cathodic protection under conditions where no hydrogen is expected, so it is reasonable to visualize the protection to be developed by reaction of the metal, possibly thru a partially protective film which is equivalent to a cell resistance rather than changing the chemistry to a hydrogen electrode. https://performancemetals.com/pages/sacrificial-anodes-faqs
Is there any evidence that metals like aluminum (or zinc or any other metals) could support a hydrogen electrode like platinum or palladium do? The standard half-cell with Pt or Pd is in 1 M HCl, which would not be appropriate for Al, Zn or Mg. Would any other conditions be better?


texts: Why ground-state configuration is consistent ("additive") from one element to the next?

texts:
Ground-state configuration ("electron shells") is consistent throughout the periodic table, for example:

(source)

Why is it this way if the Hamiltonian of each atom is different? In other words, why Al is $\mathrm{[Ne]3s^2 3p^1}$ and not something completely different: (1) at the core, and (2) at the valence.


texts: Vaporizing NOx (NO and NO2) with hot metal?

texts:
So essentially I'm looking at a product that my intuition tells me is kind of similar to a perpetual motion machine (Impossible).

Catalytic Converters use platinum, rhodium, and palladium to convert Hydrocarbons, NOx, and CO.

NOx turns into Nitrogen and oxygen.

Hydrocarbons turn into Water and carbon dioxide

Carbon monoxide into carbon dioxide.

THIS PRODUCT (see link) claims to "vaporize" "toxic fumes". It doesn't seem to explain what they turn into. just that they go away. (in the report it appears that some of it is turning into oxygen as that number goes up?)

Isn't NOx and CO already considered a vapor? how does one further vaporize it?
Simply using hot steel to convert gases seems strange but using hot platinum to convert gasses is also pretty strange when you think about it.
Is this actually a legitimately effective product?

http://www.impulsengine.com/newproducts/how-it-works_ev_muffler.shtml

http://www.impulsengine.com/newproducts/pdf/Impulse_EV16_Muffler_Emission_Results.pdf


texts: Does Photoelectric effect occur in a micro-oven while heating food?

texts: Does the photoelectric effect occur while heating food on a metal plate in a microwave oven? If not, then why doesn't it occur?


texts: What happens to particulate matter after collection via electrostatic precipitator?

texts:
What I understand about electrostatic precipitators is that the particles become ionized due to corona discharge and thus are attracted to the oppositely charge plate. This would work as long as the precipitator is turned on and plates maintain a charge.

However afterwards, when the precipitator is turned off, wouldn't the collected particulate matter tend to regain their charge neutrality? What if it goes back to its original state? Wouldn't the whole action of the precipitator then become moot?

How is the precipitated pollutant stored and prevented from escaping in an electrostatic precipitator?


texts: How is dissolving a physical change and not a chemical change?

texts: When salt dissolves in water it dissociates and it is no longer in a lattice structure. The electrostatic forces are no longer there and are replaced by water-ion interactions. To me that sounds like old bonds breaking and new bonds forming. Shouldn't the reaction look something like this? $$\ce{NaCl + H2O -> Na+ + Cl- + H2O}$$


texts: How does the production of pure, crystalline silicon via the Czochralsky or Siemens process?

texts:
I have a few questions regarding the production of pure, crystalline silicon:

As far as I know Silicon usually appears in nature in the form of sand or $\ce{SiO2}$ and then is split apart and brought into the form $ \ce{Si + 2CO} $ ;
I am imagining now a hot glowing molten mass.
However then I don't understand the following methods to separate the Si from the elements you don't want to have, like iron, carbon etc.
How do you remove the impurities, why do those methods work?
For example you use a few other chemical reaction to bring Si into several other forms like $ \ce{HSiCl_3} $ and split them apart later on.
I don't understand at the moment, how this helps to separate those materials as in: There is still this big mass with lots of different chemical connection you don't want to have.

I also lack an actual understanding of the Czochralski process to further purify your mass of silicon. I guess want has to accept that silicon likes to join pure crystalline silicon and adapt to its structure. However I don't see, why one is not using this method beforehand for example, if one already has raw silicon you get from splitting up $ \ce{SiO_2} $ if it works so greatly. And if it not does work so greatly, why don't you have other impurities ?


texts: Electrode potentials vs interfacial potential differences

texts:
Between an electrode and an electrolyte there exists an interfacial potential difference.

Many authors give the electrode potential to be the electric potential of the electrode relative to the electrolyte. I have a few problems with this, and was wondering whether anyone could help.

We define the electrode potential of SHE to be 0V. It is impossible to measure the interfacial potential difference, however nevertheless one certainly exists between the reference electrode and the solution. Are we saying that we define the interfacial potential difference of the SHE to be zero, and then have electrode potentials of other couples as interfacial potential differences measured relative to this interfacial potential difference?

To my mind, this cannot be right. Don't we just set our zero reference (i.e. one end of our voltmeter) of electric potential at the electrode of the SHE, and measure electric potentials of other electrodes relative to this?

Sergio Trasatti wrote this regarding electrode potentials,

  Equation (4.7) shows that the "electrode potential", as obtained in
  practice, does not measure the electric potential drop between the
  bulk of the metal and the bulk of the solution, but it is a more
  complex quantity which includes both electrical and chemical
  contributions.

Why do so many authors conflate interfacial potential differences and electrode potentials? Or am I missing something here? Thank you!


texts:
I need someone to back me up on this before I go confront my teacher:
I was doing some analysis of the dipole moment of cis-2-butene.
Let's say that the alkyl groups are both on top.
Would the dipole moment be a vector that has its tail on the top and its head on the bottom?

How would one calculate that?
I made some calculations assuming all C-H bonds have the same dipole moment vector and came to the conclusion that the three H's attached to the alkyl groups actually end up overcoming the dipole moments of the C-H bonds of the two unsubstituted H's on the double bond.

Am I right?


texts: Is there a relationship between viscosity and enthalpy of vaporization?

texts:
It would be useful to be able to predict relative evaporation rates of liquids.  For small reduced temperatures the heat of vaporization is relatively constant, but it is not one of the more common properties cited for substances.

Is there any sort of functional relationship between enthalpy of vaporization and common properties like viscosity, melting point, and boiling point?


texts: More effective fire extinguisher liquid than water

texts: I join robot fire fighting contest.  One of the mission is to extinguish candle by spraying it with liquid (water is default option). For spray mechanism I use pump with Venturi effect principle.  Is there any liquid substance that is more effective extinguishing fire than water by Venturi spraying mechanism? Homemade is preferred.


texts: Approximate Hamiltonian in variational method (Example of Helium atom)

texts:
As one know, the exact Helium Hamiltonian
\begin{equation}
        \hat H =
        \left( -\frac{\hbar}{2m_e}\Delta_1 - \frac{Ze^2}{r_1} \right)
        +
        \left( -\frac{\hbar}{2m_e}\Delta_2 - \frac{Ze^2}{r_2} \right) +
        \frac{e^2}{r_{12}}
    \end{equation}
Now, we can use variational method for determining approximate value of energy of ground state with $\Phi = \frac{\zeta^3}{\pi}e^{-\zeta(r_1 + r_2)}$ as
\begin{equation}
        E_{0_{\min}} = -\zeta_{\min}^2 = -\left(Z - 5/16\right)^2 = -\left(Z - \sigma\right)^2.
    \end{equation}
Can we say that we actually found the Hamiltonian for a given function $\Phi(r_1,r_2;\zeta_{\min})$ in form
\begin{equation}
        \hat H_0 =
        \left( -\frac{\hbar}{2m_e}\Delta_1 - \frac{(Z-\sigma)e^2}{r_1} \right)
        +
        \left( -\frac{\hbar}{2m_e}\Delta_2 - \frac{(Z-\sigma)e^2}{r_2} \right)
    \end{equation}
? I.e. is the such $\Phi(r_1,r_2;\zeta_{\min})$ eigenfunction of $\hat{H}_0$?


texts: Is the reasoning of spin contamination correct?

texts:
The common explanation of spin contamination is like the following:

The non-relativistic electronic Hamiltonian commutes with $S^2$ and $S_z$. Hence, the exact eigenfunction should be an eigenfunction for $S^2$ and $S_z$ operators.

However, the non-relativistic Hamiltonian has no spin variables. Any wavefunction contains spin, the spin part will commute with the Hamiltonian anyway.

For instance, in addition of angular momentum,
http://www2.ph.ed.ac.uk/~ldeldebb/docs/QM/lect15.pdf
One can form $\{J_1^2, J_2^2, J_{1z}, J_{2z}\}$ set of variables. They commute with Hamiltonian, but no longer eigenfunction of $S^2$, i.e. $\{J^2, J_z, J_{1}^2, J_{2}^2\}$.

If my argument is correct, what would be the actual justification for spin adaptation?


texts: How fast is the interconversion triplet → singlet in organic molecules?

texts:
When computational studies are performed on transition state geometries, the "thermodynamic" (that is, with no kinetic considerations) energy of the analyzed state is obtained.

I was wondering: if a (multistep) reaction begins in a biradical state, the kinetics of the interconversion from triplet to singlet is so slow that the reaction is likely to proceed in a radical fashion, or if a lower transition state exists for the ionic (singlet) counterpart, then it is likely to proceed in a ionic way, because the rate of interconversion is extremely fast?

I am sorry if the question is dumb, but all I could find was about transition metals, and I don't know if the same applies.


texts: Why is the top SN2 reaction faster? (Molecular Orbital Theory)

texts:
I'm having trouble understanding why the top SN2 reaction proceeds faster. I know that benzylic and allylic halides react faster in SN2 reactions than non-conjugated halides. I think it's because the transition state is more stable but how can you explain that using MO Theory?

  This is what my professor drew for this question but I don't understand it all. Any help would be appreciated :)


texts: Determining concentration of phosphate buffer from pH?

texts:
I bought a phosphate buffer from Sigma/Fluka (73212-1L) containing potassium dihydrogen phosphate ($\ce{KH_2PO_4}$) and disodium hydrogen phosphate ($\ce{Na_2HPO_4}$).

It is at pH 8.0 but they do not provide the phosphate concentration. Can I determine it from pH via titration?

This table shows the concentrations for a 0.2M solution:
http://www.sigmaaldrich.com/life-science/core-bioreagents/biological-buffers/learning-center/buffer-reference-center.html#phosphate


texts: Does K2CO3 react in minute amounts with glassware at higher temperatures?

texts:
At a temperature of $\pu{750 ^\circ C}$, $\ce{K2CO3}$ and $\ce{SiO2}$ react with each other in substantial proportions, forming $\ce{K2SiO3}$ and $\ce{CO2}$ in the process$\ce{^{[1]}}$.
We all know as well that potassium hydroxide reacts with glass. So, I was wondering if $\ce{K2CO3}$ was reacting with pyrex and/or normal glass in minute amounts, either in solution at say >$\pu{150 ^\circ C}$ or when being dried under vacuum in an oven.
One putative indirect mechanism in my wild imagination would be if $\ce{CO2}$ could leave the solution (maybe only at higher temperatures) and if potassium hydroxide at all existed in solution, upon the dissolution of $\ce{K2CO3}$ in water?
References:

Shikha Agarwal, In Engineering Chemistry: Fundamentals and Applications;  Cambridge University Press: Delhi, India, 2016 (ISBN: 978-1-107-47641-7).


texts: How is Negative Temperature Hotter than Infinite Temperature?

texts:
Recently I have read articles stating that negative Kelvin has been achieved. I was a bit speculative at first as I though how can you get cold than 0 Kelvin, but after doing some research it makes sense on how this is possible.

However the one thing that I still not sure is that it stated that the temperature scale can't be thought as being linear but rather as a loop which goes in the following order, "+0 K, … , +300 K, … , +∞ K, −∞ K, … , −300 K, … , −0 K".

How can negative Kelvin be hotter than infinite temperature?


texts: VSEPR theory and hybridization in determining the shape of a molecule

texts:
Our chemistry teacher told us that both VSEPR theory (which says that the electron pairs in the valence shell of an atom arrange themselves in such a way that repulsions among them are minimized and this arrangement of the electron pairs determines the shape of a particular molecule)  and hybridization (which is the intermixing of a particular number of atomic orbitals to form equal number of new orbitals which have same shape and energy)  can be used to determine the shape of a molecule and that they are independent of each other. I understand how the shape of a molecule can be predicted using the VSEPR theory but i cannot understand how hybridization helps in determining or rather predicting the shape of a particular molecule. I have searched the net but could not find any useful resource.

How does hybridization help in determining the shape of a molecule?


texts:
Why does the alkoxide anion dont act as a nucleophile in the fevorskii rearrangement?
It can displace halide as halide is alpha to carbonyl and carbonyl decreses the energy of c-halide lumo


texts: Solubility of salt in heavy water vs. "regular" water

texts:
I would like to know if salt can be dissolved in heavy water ($\ce{D2O}$) as it would be in normal water ($\ce{H2O}$).

If so, what will the maximum salinity be in $\ce{D2O}$? I know the maximum in $\ce{H2O}$ is about 26% of salt by mass.


texts: How do you draw (E)-1-phenyl-1,3-butadiene?

texts: I'm having trouble drawing this molecule because I don't understand how the functional group Phenyl (by -ene suffix) can also be a substituent (by 1-phenyl). Also, what does the 1,3-butadiene mean?


texts: Using MO theory, give an explanation for the C-C bond length in cyanogen

texts:
1. The problem statement, all variables and given/known data

2. The attempt at a solution

I know that the MO diagram for CN- is this:

I am unsure how to draw the MO diagram for cyanogen. I know that the higher the bond order, the shorter the bond length. I have tried to draw a MO diagram for cyanogen by combining two of the MO diagram for CN:

Not sure if this is necessary but I have drawn the following resonance structures:

I think that structure (I) contributes the most as structures (II) and (III) have a positive charge on the nitrogen.

I think the C-C bond in cyanogen is shorter than the "usual" C-C bond lengths due to delocalisation across it but I don't know how to explain this using Molecular Orbital theory.


texts: I was wondering how scientists are able to handle atoms. They are very small, but surely people are able to interact with them somehow? The Large Hadron Collider is one example. Also, they try and make new elements by mixing atoms together. How are they able to handle something so small?


texts:
$\ce{K2CO3}$ doesn't boil. It thermally decomposes at $\pu{1200 ^\circ C}$. However, I find conflicting information online about this. Roughly what I have found say three inconsistent things:

It doesn't decompose
At $\pu{1200 ^\circ C}$, it decomposes into $\ce{K + O + CO}$
(Chemiday)
At $\pu{1200 ^\circ C}$ it decomposes into $\ce{K2O + CO2}$ (allreaction)

What actually happens when $\ce{K2CO3}$ thermally decomposes? Most sources agree with (3). But how can that be? Wouldn't it just decompose some more? $\ce{K2O}$ decomposes at $\pu{300 ^\circ C}$ into ($\ce{K2O2 + K}$) and $\ce{K2O2}$ decomposes back into ($\ce{K2O + O2}$) at $\pu{500 ^\circ C}$.
What is going on here? Is $\ce{K2O2}$ really decomposing back again to $\ce{K2O}$? If so, then at $\pu{500 ^\circ C}$ do both of these decompositions occur, cyclically pumping out $\ce{O2}$ and $\ce{K}$?
I read elsewhere that at temperatures over $\pu{500 ^\circ C}$, $\ce{K2O2}$ decomposes into ($\ce{2K + O2}$). This would resolve the conflict. But I find the source is unreliable. What is right?


texts:
In this reaction,
$$\ce{KIO_3 + KI -> I_2}$$
According to law of chemical equivalence, shouldn't $m_{eq}$ of $\ce{KIO_3}$ = $m_{eq}$ of $\ce{KI}$ = $m_{eq}$ of $\ce{I_2}$?
However, the book that I was reading from, said:
Total $m_{eq}$. of $\ce{I_2}$ = $m_{eq}$ of $\ce{I_2}$ (from $\ce{KIO_3}$) + $m_{eq}$ of $\ce{I_2}$ (from $\ce{KI}$).
Why is it so?


texts: Is [Co(NH₃)₄Cl₂]Cl paramagnetic or diamagnetic?

texts:
$\ce{NH3}$ is known to be a strong field ligand, while $\ce{Cl}$ is known to be a weak field ligand.

Is $\ce{[Co(NH3)4Cl2]Cl}$ a high spin complex or a low spin complex?

I assumed this to be a high spin complex. Oxidation state of $\ce{Co}$ is $+3$.
And electronic configuration of $\ce{Co(III)}$ is $\mathrm{[Ar]~3d^6}$.

Since I assumed this to be a high spin complex — pairing of electrons of $\mathrm{3d}$ orbitals will not happen. The $6$ pairs of electrons from the ligands must be included in the $\mathrm{4s}$, $\mathrm{4p}$, $\mathrm{4d}$ orbitals — which leaves electrons unpaired in the $\mathrm{3d}$ orbital, making this a paramagnetic complex, with hybridisation $\mathrm{sp^3d^2}$.

Answer given to this question says otherwise. Hints are welcome!

This question is an excerpt of a question that appeared in the JEE(A) - 2016


texts: However what is so acidic about CaO and basic(no pun intended) about SiO2 while calculating basicity of slag?

texts: I have seen Basicity to be calculated as $\mathrm{B} = wt\%\:\ce{CaO}/wt\%\:\ce{SiO2}$ particularly in slag bascity/acidity calcuations. Now I do not think that $\ce{CaO}$ is the most basic oxide that we have or $\ce{SiO2}$ is the most acidic oxide then why are they calculated accordingly? On a lighter note in my geology classes, I have been taught to classify minerals as acidic on the basis of Silica content. Are they related? Please explain with close reference to context.


texts: How is a phase equilibrium defined for a one-component system?

texts:
A question on this site asked whether a one-component system is at equilibrium when melting or boiling, and the disparate answers were somewhat dependent on the definition of phase equilibrium. Another question asks whether two phases can ever exist in equilibrium at the boiling point. The term "phase equilibrium" seems to imply that under certain conditions, a one-component system with two phases is indeed at equilibrium.

Searching for the definition of phase equilibrium, I found these two:

Definition 1

  Phase equilibrium is the study of the equilibrium which exists between or within different states of matter namely solid, liquid and gas. Equilibrium is defined as a stage when chemical potential of any component present in the system stays steady with time.

Source: https://www.wattco.com/casestudy/phase-equilibrium

Definition 2

  Phase equilibrium is the state of thermodynamic system, in which the different phases of the substance having common boundary surfaces do not vary quantitatively.

Source: https://www.elsevier.com/books/computational-materials-science/ovrutsky/978-0-12-420143-9

Implications of the distinct definitions

According to definition 1, water present as two phases at the melting point would be at equilibrium even if slowly melting isothermally. According to definition 2, the same situation would not be called equilibrium because the amount of ice is decreasing over time (and thermodynamic parameters such as entropy and inner energy are changing over time).

Phase rule

For the mentioned system, the phase rule specifies one independent degree of freedom (you can change one intensive parameter, say temperature, and all other intensive parameters, in this case just pressure, will be determined, given that the system is supposed to be at equilibrium). Because it is a one-component system, the concentrations (or activities) are constant and are not a degree of freedom. If you are used applying the equilibrium concept to solution chemistry, this is somewhat unusual.

Question: What is the official definition of phase equilibrium, and how does it apply to a one-component system where the chemical potentials are independent of the mole ratios?


texts: What is the reason for anomalous expansion of water? Why doesn’t it simply expand on heating or contract on cooling? Why it shows anomalous behavior at 4 degrees Celsius? Why not on 4.6 or 10 (or whatever) degrees Celsius?


texts:
I used normal paper from my notebook to perform filtration. The filtration is 100% perfect, but takes incredibly long to happen, because the paper is too dense.

I'm not planning to buy filtration papers. They're cheap, but I don't filter something every day, so they'd be laying around useless. I would prefer to be able to use some household item as a filtration paper.

One idea I had was to apply some substance on normal writing paper to make it softer.

I have tissues which are very soft, but these are too soft and will leave paper chunks in my filtrate.

Do you have any idea what should I use for filter paper, or how could I alter normal paper to suit my needs?


texts:
Here, this is a 1° allylic halide. If it goes by SN1, the intermediate will be resonance stabilised.

Also, since it is 1° Halide, it can also go via SN2. Which one will be preferred?


texts: Is (2R,3S)-3,4-dimethylpentan-2-ol feasible to be dehydrated with POCl3 and pyridine?

texts:
I was given a problem of reaction between (2R,3S)-3,4-dimethylpentan-2-ol and $\ce{POCl3}$ and pyridine. I know that $\ce{POCl3}$ will be attacked with hydroxyl group and the hydrogen on hydroxyl will be cleaved with pyridine so the hydroxyl group becomes good leaving group.

The reaction mechanism proceeds on E2 mechanism no matter whether the alcohol is primary, secondary, or tertiary. The problem is E2 mechanism can proceed if the stereochemistry of antiperiplanarity is fulfilled. When I drawn the stereochemistry of the alcohol, it turned that methyl on alpha-carbon and beta-carbon made the beta-hydrogen on these carbons cis to the hydroxyl group (the methyl on alpha carbon is wedge so the bonded hydrogen and hydroxyl group are dash), thus the reaction can not proceed.

Is that correct? If it is correct, will the reaction mechanism proceed on other mechanism?


texts:
(It was the Winterbash icon that got me thinking on this.)

Snow flakes take on a variety of intricate shapes, but what processes are responsible for this?

(Got the image off of Wikipedia)

I mean, I wouldn't have raised this question if those water droplets, descending towards earth, assumed a... less fancy shape. Not only are these minuscule structures very intricate, they also display a high degree of symmetry (with most having multiple planes of symmetry).

Now, as I understand it, all processes proceed so as to maximize the "randomness" of its constituent particles. (Oversimplified version of the Second Law of Thermodynamics, yes, I know... just don't chew me out in the comments section...)

This Law can easily be observed in, and verified by, natural processes.

Now the formation of snow is a natural process, agreed? The way my brain sees it, is that water droplets ought to freeze into random, and by virtue of its "randomness", highly unsymmetrical shapes. But this is not the case here!

For some confounded reason, the shapes assumed by snowflakes are eerily symmetrical. So eerie, that I'm surprised it hasn't attracted the attention of conspiracy theorists yet, as in the case of crop circles. Now I'm not saying you don't find symmetry in nature, there're plenty of examples out there. But what I am trying to point out here, is that you don't typically see symmetry to such a high extent as in the case of snowflakes.

There are innumerable natural processes that give rise to weird shaped stuff, but I'm not really sure what makes snowflakes so different. However, I did notice a few points of difference between the formation of snowflakes and other natural processes:

1) As water droplets/snow descends, it's subjected to significant temperature changes as it passes through different layers of the atmosphere.

2) As water droplets/snow descends, it's subject to a significant increase in pressure as it passes through different layers of the atmosphere.

So, I reiterate my question.

Why are snowflakes shaped as they are?

Spin-off question:

I heard (not sure where) that each snowflake assumes a unique shape. How true is this?


texts: What happens in the NH4Cr2O7 with HgSCN reaction?

texts:
Apparently this video is a reaction of $\ce{NH4Cr2O7}$ with $\ce{HgSCN}$.

The title of the video suggests the reaction opens a portal to hell, but I am pretty sure that is not the case.

What exactly goes on in the reaction?


texts: Sublimation and recrystallization of caffeine

texts:
I'm looking to do an extraction of caffeine from energy drinks. I want to use both sublimation and recrystallization in my experiment for advanced purity.

My question is which should happen first, recrystallization or sublimation? Does it even matter which happens first?


texts: Why is an energy cost associated with splitting the HOMO spins in singlet oxygen?

texts:
The molecular orbital schemes for both forms of singlet oxygen ($\mathrm{^1\Delta_g}$ and $\mathrm{^1\Sigma_g^+}$) and triplet oxygen ($\mathrm{^3\Sigma_g^-}$) are typically given as shown in the image below.

Figure 1: Molecular orbital schemes of two types of singlet oxygen and triplet oxygen with the highest energy electrons highlighted in red.

Hund’s rule sufficiently predicts that the triplet $\mathrm{^3\Sigma_g^-}$ state is the most stable, i.e. lowest in energy. When one speaks of singlet oxygen, one typically has the $\mathrm{^1\Delta_g}$ form in mind which is $\pu{0.98eV}$ higher in energy than triplet oxygen according to a group member’s recent literature seminar. This is often explained on this site by the fact that spin pairing puts another electron into the space that is already populated by one electron, causing electron-electron repulsion that must be overcome by adding energy.

Extending this explanation, I am inclined to think that the $\mathrm{^1\Sigma_g^+}$ form of singlet oxygen, whose MO scheme is depicted in the centre of figure 1, should have a lower energy than the $\mathrm{^1\Delta_g}$ form because the spins are occupying spacially different (and orthogonal) orbitals. However, the same seminar talk also included the energy difference of $\pu{0.65eV}$ between $\mathrm{^1\Delta_g}$ and $\mathrm{^1\Sigma_g^+}$ with the $\mathrm{^1\Sigma_g^+}$ being higher in energy.

Why is this so?


texts: Liquid alternative to alcohol to lower density of water

texts:
I am trying to create a suspension of polypropylene particles in a water based liquid. I want the density of the liquid to be more than or equal to the density of polypropylene (855 - 946 kg/m3) so that the particles don't float or sink too easily. It doesn't have to precisely match, just be close. I had thought of using alcohol, but the problem there is that I need to house the suspension in a container made from either acrylic or polycarbonate, which are both not very resistant to alcohols.

What I'm trying to find is a safe and hopefully cheap liquid that can lower the density of water but not attack acrylic or polycarbonate.

Thanks


texts: Why are allyl halides reactive towards both SN1 and Sn2 reactions?

texts: I know that allyl halides are reactive towards SN1 reactions due to the stabilization of carbocation due to resonance but why are they reactive towards SN2 too?


texts: Total number of isomers formed on monobromination of 2-methylbutane

texts:
What is the total number of isomers formed on monobromination of 2-methylbutane (including configurational and stereoisomers)?

I tried working it out. However, I found only five:

According to the source, the answer is six. Which structure am I missing?


texts: What is the difference between reactant and reagent?

texts: What is the difference between reactants and reagents? I've seen both used for very similar situations... The dictionary said that reagents are added to a reaction to identify another substance, but wouldn't that be an indicator?


texts: H NMR signals in 1,4-dichlorobutane spectrum

texts: I have come across H NMR spectrum of 1,4-dichlorobutane and I have noticed that signals there are different to what I would intuitively expect. Instead two triplets there are two multiplets of more complicated structure. I wonder why that is. Looks to me like some higher order spectrum, but I'm not sure. I don't think that is the matter of spectrometer frequency. I wonder if that is some instance of magnetic inequivalence (at the first glance in 1,4-dichlorobutane there are two sets of methylene groups with enantiotopic hydrogen atoms). Can someone clear that out for me?


texts: What's the definition of multi phase materials? Does it mean the different phases represent different materials?

texts:
I'm from a CS background and just trying to understand the real meaning behind multi phase materials. Following is the experiment which drove me towards this question.

With the help of DFT and machine learning, we identified that the material LaBiO3 could display interesting dielectric properties. Hence, a team here mixed the oxides in stoichiometric ratio in a ball mill and observed the XRD patterns of the formed composite powder.

The XRD data suggest that LaBiO3 is unstable and form Bi1.4La0.6O3 R-3m phase and Bi2La4O9 R3m phases.

So my question is, is this a composite that has nothing to do with LaBiO3 and they are just two different materials? Or could this be categorized as a metastable phase of LaBiO3?

Could anyone explain this with the definitions?


texts: How to calculate the mass of water to add to copper(II) sulfate to form a 4% solution?

texts:
How many grams of water are required to make a $4.00\%$ solution with $15.0~\mathrm{g}$ of copper(II) sulfate pentahydrate?

I calculated the percent composition of water in a molecule of $\ce{CuSO4.5H2O}$ and it came out to be $36\%$. From that I calculated that there was a total of $5.4~\mathrm{g}$ of water in the sample. I'm guessing that we have to calculate how much water is required in order to make it a $4.00\%$ solution, but I don't understand why it wants it in grams. When
$$\text{Percent by volume} = \frac{\text{grams of solute}}{\text{mL of water}}?$$


texts: What is the rationale for calling something as an 'inorganic [organic compound]'?

texts:
While studying the main groups of p-block, I have seen many compounds being labeled as an analog to some popular organic compound. For example, borazine is termed as 'inorganic benzene', while boron nitride has been called 'inorganic graphite'.
Now, my question is, whether these monikers (if that's what they may be called?) reflect just the structural likeness, the chemical similarities or, perhaps, both?
Moreover, are there some other examples which illustrate this?


texts: Why does gilman reagent react with acyl chlorides but not with other carbonyls?

texts:
According to HSAB (hard-soft acid-base) concept, a soft nucleophile preferentially reacts with soft electrophile and a hard nucleophile with a hard electrophile.

Since $\ce {R2CuLi}$ is a soft nucleophile it should react with ketones or aldehydes rather than acyl chlorides since acyl chloride should have higher positive charge density due to combined effect of chloride and oxygen.

I still don't understand HSAB completely as I don't know much about concept of orbitals. But I think acyl halides should have higher positive charge density at the carbonyl carbon.


texts: The color of resorcinol-formaldehyde resin

texts: At school, I did an experiment of synthesizing resorcinol-formaldehyde resin. When I added $\ce{NaOH}$ and gave some heat, the color of resorcinol-formaldehyde resin inside the test tube became reddish-brown. Can anyone tell me why?


texts: Does a unit cell have to contain a whole number of atoms?

texts:
I was given this problem recently to compute the number of ions in a unit cell of ferrous oxide $\ce{FeO}$. The data given was:

Side length $a = \pu{5 Å}$
Density $d = \pu{4 g/cc}$

Using the formula $\displaystyle d = \frac {ZM}{N_0 a^3}$, I obtained $Z = 4.18$. However, the answer had rounded $Z$ off to $4.$
Could a unit cell have  a fractional number of atoms? Intuitively, it doesn't make sense for a cell to have $0.18$ of an atom. If, by experimental analysis, we obtain a fractional number of atoms in a unit cell, do we round them down as is done in this problem?
P.S. Another thought would be that such odd numbers are obtained due to stoichiometric defects.


texts:
I am confused about what seems to me two very different explanations for the relativistic contraction of orbitals for heavy elements.
My teacher told me that since 1s electrons in heavy elements travel very fast their momenta is much larger than predicted by classical physics. Hence the 1s orbital contracts lead to the contraction of all ns orbitals so that their overlap continues to be zero. D and f orbitals on the other hand do not contract. Because of their symmetry, they do not need to contract for overlap with the 1s orbital to remain 0. They in fact expand because of increased shielding from s electrons.
My book however says the reason for the contraction is that since ns orbitals are non-zero at the nucleus they experience the effects of nuclear charge more and hence relativistic contraction is most significant in them (it as if implies that the ns orbitals are all traveling at relativistic speeds). Which one is correct? Or are both of them oversimplifications?


texts:
I have often studied the reaction of Br2/CCl4 with But-2-ene which results in formation of

But I wondered what would be formed if Cl2/CCl4 reacts with But-2-ene. Does it lead to the formation of
This:
Or This:
Or something else which I never expected


texts:
There are 2 double bonds $\ce{C=C}$ present within each piperic acid molecule,  thus when piperic acid reacts with hot excess $\ce{KMnO4}$, it oxidised into a carboxyllic acid. Why is $\ce{CO2}$ produced?

The carbon atom bonded directly to the benzene ring will get oxidised into a carboxylic acid and also that the carbon bonded to the $\ce{COOH}$ group will get oxidized also to a carboxylic acid to form a dicarboxylic acid. What changes will take place to the other 2 carbon atoms.


texts: Removing diamonds from a 14 karat gold ring with acid

texts:
I have a 14 karat gold ring with diamonds. I want to weaken the metal (to get the diamonds out without damaging them).

If I dip the ring in sulfuric acid, will I be able to dissolve the base metal in the alloy leaving the gold in place?


texts: Home test for the presence of sugar in erythritol

texts: Is there a test to distinguish erythritol from sugar at home without expensive lab equipment or exotic reagents?  Sometimes I purchase erythritol online and wonder if it's been diluted with sugar.


texts:
By definition,

  dS=dqrev/T.

Based on my understanding, the subscript rev means that the dq is heat exchanged in a reversible pathway from a state i to another state f, regardless of the actual pathway by which the process proceed. I am always curious why ΔS is defined only for reversible process, it would be good if someone can explain it, nonetheless it is not our main concern here-let's just accept the definition first.

So, similarly,

  dSsur=dqrev,sur/Tsur......(1)

From what I have read, V of surrounding can be regarded as constant, so

  dqrev,sur=dUsur

and since dUsur is a state function,

  dUsur=dqsur

and therefore dqrev,sur=dqsur implying

  dSsur=dqsur/Tsur......(2)

(a) If V is constant, q=ΔU, so q is a state function at constant V?

(b) Let's stop at equation (1). Suppose we would not like to simplify it further, and since the equation (1) is an intermediate result it must be true, we have

  dS=dqrev/T and

  dSsur=dqrev,sur/Tsur

I suppose dS without any subscript is dS of system. By First Law,

dqrev= -dqrev,sur

and then if T=Tsur and the chemical reaction has not reached equilibrium (is this scenario possible?),

  dS= -dSsur

By summing up all entropy changes for system and surrounding, we have
ΔStotal=0 for non-equilibrium state? But as I know ΔStotal=0 if and only if surrounding is in equilibrium with system. What's my misconception here?

(c) How can dqsur,irrev=dqsur,rev? Does not make sense for me physically, without looking at the equation with dUsur


texts: My EDTA titration isn't giving the right titre

texts:
I am, as a fun off-syllabus investigation, looking at hard water and how effective the EDTA titration method is, for permanent and temporary hard water.
I ran a titration today and had horrific results. I actually knew the concentration of my water sample: $\pu{0.005 M}$ made up with $\ce{Ca(NO3)2}.$ My EDTA was $\pu{0.01 M}.$
I'm clearly looking at a $1:1$ ratio between $\ce{Ca^2+}$ ions and EDTA molecules. I had $\pu{50 cm^3}$ in my conical flask, so at this concentration, I'd expect my titre to be about $\pu{25 cm^3}.$ I added a little Eriochrome Black T, 8 drops of $\mathrm{pH}~10$ buffer, and my colour change was more or less instant.
If I'd actually bothered to work out that I should aim for a $\pu{25 cm^3}$ titre, I wouldn't have wasted my time but instead, I diluted my EDTA to $\pu{0.001 M},$ and my next few titres were $\pu{4.8 cm^3}.$
Now, I know very little about the buffer. Am I putting far too little in? Or is my EDTA actually, $\pu{0.5 M}$ instead of $\pu{0.01}?$


texts: Does 1,3-diphenylprop-2-en-1-one give a positive Tollens test?

texts:
If we have 1,3-diphenylprop-2-en-1-one, will it give positive Tollens test? I think aldol reactions are reversible under basic conditions. Here there are mildly basic conditions, so will we get back the reactants of the aldol reation?

This question was part of JEE ADVANCED 2016 where they asked which will give Tollens reagent test. I feel it has mildly basic conditions for KOH, hence it should perform reverse aldol and thus this should be the Answer. But the official answer key says no.

Please help me out because I can't understand how to distinguish between the two types.


texts: Formation of toluene from (cyclobutane-1,2,3-triyl)trimethanol using conc. sulphuric acid

texts:
In my book this reaction is given without any mechanism:

I thought that simple dehydration reaction is going to take place with rearrangement of the carbocation but I have no idea as to how toluene turned out to be the product.


texts: Lewis Acid / Base reaction for SO2 and H2O

texts:
I am having trouble with this question:

Identify the Lewis acid and Lewis base in each of the following
reactions:

$\ce{SO2(g) + H2O(l) = H2SO3(aq)}$

What I tried:

A Lewis acid is an electron pair acceptor.

A Lewis base is an electron pair donor.

The other problems of this type involved cations or anions, so I was able to identify the cation as the Lewis acid and the anion as the Lewis base.

However, this question does not involve ions.  So I tried to look at the lone pairs on the molecules.  Since they both have lone pairs, I figured since $\ce{SO2}$ has more lone pairs, it would act as the Lewis base.  Also in the final molecule, the hydrogen atoms would be bonded to two separate oxygen atoms, so I thought of them as migrating to the lone pairs on the $\ce{SO2}$ oxygen atoms.

However, the textbook says that $\ce{SO2}$ is the Lewis acid and $\ce{H2O}$ is the Lewis base.

Why would this be the case?


texts: why doesn't dz2 orbital have any nodal plane?

texts: why dz2 orbital does not have any nodal plane whereas the other orbitals such as dxy and dzy have nodal plane? As l=1 , won't it have at least one angular node?


texts: Why is the carbon dioxide we exhale transparent?

texts: Why is carbon dioxide that comes from dry ice opaque and smoky while the carbon dioxide that we exhale transparent?


texts: If two electrons move up to a higher energy level in an atom, is it considered excited?

texts: In Germanium, if two electrons go from 1s go to 4p is it in its excited state?


texts: How many hydrogen bonds in these compounds?

texts:
We usually get some questions about how many hydrogen bonds these compounds can create, we use it to differentiate between the boiling point of each one of them so it would be great if you could help me.

So what I know that $\ce{H2O}$ has 4 hydrogen bonds those are 2 from hydrogen atoms and 2 from other molecules that has 2 hydrogen atoms connected to the 2 lone pair of electron that the oxygen has.

In $\ce{HF}$, It has 2 hydrogen bonds. The same explanation implies here.
In $\ce{NH3}$, 2 hydrogen bonds because $\ce{N}$ doesn't have the required amount of lone pairs to make more hydrogen bonds.

But what I really want to know is about alcohols. In the way that I am explaining it, it should have 2-3 hydrogen bonds but when I check some books and articles they say that it only creates 1.

So if you can explain how many each of them creates and what it depends on that would be awesome.


texts: Relationship between the water ionization constant and ionic strength

texts:
I read in a textbook that

  the water ionization constant ($K_\mathrm{w}$) increases as the ionic strength of the solution increases

and it confused me. If the ionic strength increased, then the activity of each of the ions $\ce{H3O+}$ and $\ce{OH-}$ would decrease, leading to a decrease in the value of $K_\mathrm{w}$.

Can someone please explain the mistake in my way of thinking?


texts: In Hoffmann's rearrangement of acid amide...the OH from the basic medium attacked the H ..now my question is...isn't the carbonyl carbon more acidic as it's surrounded by 2 electronegative elements?


texts: How to get the coordinates or .cif file of β  and χ ?

texts:
Can someone tell me how to draw the β  and χ  in Materials Studio or any other software? I've just started my project work, and I'm a beginner in this field.
I have searched for the coordinates or .cif file in the literature, but I could not find any. If anyone can provide me with those, it'll also be helpful for me.


texts:
In the last few decades, many alkalides - anions of alkali metals - have been synthesised. The most famous is undoubtedly that of sodium: $\ce{[Na(\text{2.2.2-cryptand})]+Na-}$, but the alkalides $\ce{K-}$, $\ce{Rb-}$, and $\ce{Cs-}$ are all known. However, $\ce{Li-}$ is not.

James Dye writes in a 1984 review1 that for the product of the reaction

$$\ce{M(s) + N(s) + L(s) -> [ML]+N-(s)}$$

to be thermodynamically stabilised ($\ce{M}$, $\ce{N}$ are metals, and $\ce{L}$ is the macrocyclic ligand), several criteria must be met:

  Small lattice energies for $\ce{L(s)}$, $\ce{M(s)}$, and $\ce{N(s)}$ so that the enthalpies of sublimation will not be too large.
  Low ionization energy of $\ce{M}$.
  High electron affinity of $\ce{N}$.
  Large complexation energy of $\ce{M+}$ by $\ce{L}$.
  Large lattice energy of $\ce{[ML+]N-}$ (which depends mainly on the interionic separation).

From these given factors, I suppose the only possible explanation is the larger heat of sublimation of lithium. However, lithium is still known to form electrides in solution - compounds of the form $\ce{[ML+]e-}$. In order for these to be formed, the sublimation energy of $\ce{Li}$ still has to be overcome.

Is there a thermodynamic reason why lithides, $\ce{Li-}$, have not yet been made?

Reference

Dye, J. L. Electrides, negatively charged metal ions, and related phenomena. Prog. Inorg. Chem. 1984, 32, 327–441. DOI: 10.1002/9780470166338.ch4.


texts: What is the IUPAC name of this organic compound?

texts:
Variety is the spice of life. I have made an organic compound myself. Can you please tell me the name?
I thought that the correct answer is -
3,3-dibromo-2,4-dichloro-1,4-difluoro-2,4-diiodo-1-methylbutan-1-ol, because the haloalkane group is to be given in the alphabetical order and the priority of the alcohol group is higher than the haloalkanes.
Is it correct? What will be the derivation of the name if the alcohol group is replaced with hydrogen?


texts: Prediction of enantiomeric excess through kinetics

texts:
Suppose we have a reaction such as the one represented above. Is there a method to estimate enantiomeric excess of the product if the rate constants are known and the product does not isomerize (and the other stereocenter doesn't either)?

To simplify, let us suppose that $a=100$, $b=900$, $c=50$, $d=30$.

We will begin with a racemic mixture (of the first two compounds). Methods that I've tried so far seem inadequate to approximate enantiomeric excess.


texts: Products of the oxidation of 1,4-dimethylcyclohexane

texts:
I am having difficulty identifying the second product. Is it an ether, or a kind of epoxide? I am out of ideas on how to reach it.

However, I do have a general idea how to receive the first product, in the means of knowing that I have to first turn the 1,4-dimethylcyclohexane to an alkyl halide and then into an alkene and then an epoxide.

I would be grateful to receive an idea of how to start.


texts:
It has been such a long time, that I totally forgot how it works.

I am interested in the charge of jasmonic acid at different concentrations.
More specifically, I want to know at what pH my molecule has no charge (or I should rather say jasmonic acid would occur as a zwitter ion).

Only the decaboxylic group can be deprotonated at higher pH.

Is it correct to assume that most of the time, when you have an
acidic compound it would predominantly occur in a nonionic form?
Does the $\log{D}$ say anything about this? does the maximum
$\log{D}$  value corresponds to the pH at the iso electric point?

If we would take aspirin for example

https://disco.chemaxon.com/apps/demos/logd/

at what pH should I expect the uncharged version?


texts: Base catalyzed rearrangement of an alkyl substituted cyclopent-2-enone

texts:
I have been asked to provide a mechanism for the following transformation:

I don't see any viable way to make this happen. All I can see that is possible is the formation of an acetal or a Michael addition. Neither of which seem useful. Can you help?


texts: Alkali metal carbonates, their thermal stability and solubility

texts: From Li to Cs, thermal stability of carbonates increases. From Li to Cs, due to larger ion size, hydration enthalpy decreases. So, solubility should decrease from Li to Cs. But, experimentally, order is reverse. I cannot wrap my head around this.


texts: I've found that a reason for people to oppose supersonic aeroplanes was the $\ce{NO_{$x$}}$ gases it released would do harm to the ozone layer. So what is the mechanism of this?


texts:
How to find the half equivalence point knowing the pH, molarity, titrant added at equivalence point?

This a fairly straightforward and simple question, however I have found many different answers to this question. I originally thought that the half equivalence point was obtained by taking half the pH at the equivalence point. However, I have encountered some sources saying that it is obtained by halving the volume of the titrant added at equivalence point.


texts: How do I remove free biotin after biotin-protein conjugation?

texts:
I want to quantify a biotin-protein conjugate after chemical biotinylation. After biotinylation, the solution contains both biotinylated protein and free biotin.

I intend to use a HABA-avidin biotin quantitation kit like this one from Pierce. Since the biotinylated protein and the free biotin will both displace HABA and decrease the absorbance, I need to remove the free biotin so that I only quantify the biotinylated protein.

How do I separate the free biotin from the solution?


texts:
Can a specific bond be broken by an engineered energy wave corresponding to the bond length?

For example, can we break the $\ce{C-N}$ bond and not the $\ce{C-H}$ in a hydrocarbon chain?


texts: What is the group reagent for the zero group (ammonium cation) in inorganic salt analysis?

texts:
Some texts suggest sodium hydroxide is the group reagent for the zero group.

However, some say there's no group reagent for zero group

So which one's right?


texts: What allows all 3 states of H₂O to be present at the same time?

texts: How is it possible for there to be a glacier floating on water but under clouds? Depending on the temperature, shouldn't there only be one state of water?


texts: Understanding Gibbs free energy and enthalpy

texts:
Let's say that a reaction releases -50kJ/mol of Gibbs free energy (delta G), and -75kJ/mol of enthalpy (we know that -25kJ/mol went to make sure that the total entropy of universe increased).

Now let's say we reversed the reaction.

Book says that the minimum energy required to make the reaction occur spontaneously in the reverse direction is the negative of the original change in Gibbs free energy (50kJ/mol).

What bothers me here is that I would think that you would need 75kJ/mol to reverse the reaction - the total energy the original reaction emitted needs to be put back in order to bring the system back to it's original potential energy level. It seems as though enthalpy shows that one amount of energy is needed to reverse the reaction, while Gibbs potential energy indicates a different amount of required energy.

I have no problem solving any of the computational problems relating to these concepts, but I'm curious about how to more fully understand them conceptually. I've noticed that a lot of people are great at solving technical problems related to these concepts, but are not too worried about how to interpret them conceptually. I guess for me, on the other hand, it's more important to understand than to compute...

Thank you for your help!


texts:
I am working with the protonation of guanidines.

The structure of these compounds looks like this:

I know that possibly the protonated-nitrogen will be the double bonded one (that structure conserve resonance), but i am looking for some experimental or theoretical proof, and it is not being easy to find a nice one. Ideas or links about this problem (maybe a paper) will be helpful.


texts: Why does two phenylhydrazine molecule react with glucose in osazone formation?

texts:
From Wikipedia:

  It involves two reactions. Firstly glucose with phenylhydrazine gives glucosephenylhydrazone by elimination of a water molecule from the functional group. The next step involves reaction of one mole of glucosephenylhydrazone with two moles of phenylhydrazine (excess). First phenylhydrazine is involved in oxidizing the alpha carbon to a carbonyl group, and the second phenylhydrazine involves in removal of one water molecule with the formyl group of that oxidized carbon and forming the similar carbon nitrogen bond.

Why doesn't it first react with the formyl group and stop with just one phenylhydrazine? That is, why doesn't the nitrogen of phenylhydrazine attack the $\mathrm{sp^2}$ carbonyl carbon (a nucleophilic addition reaction)?

Why does it oxidize glucose first and then proceed?


texts: Effects of Groups on the Nucleophilcity of Nitrogen

texts:
The reactivity of nitrogen mustards increases with increasing
  nucleophilicity of the central nitrogen atom. Select the most and least reactive from each of the following groups of nitrogen mustards.

My Attempt

I know that II will be the most reactive since the methyl group will donate electron density to the nitrogen atom due to inductive effects, making it more nucleophilic and hence more reactive.

I also thought that III will be the least reactive since the ester group pulls more electron density away from the nitrogen atom compared to the carbonyl group. I also thought in general that esters are stronger deactivators than carbonyl groups. However the answer is I.

After searching on the internet, it turns out that esters and carbonyl groups are roughly equally strong deactivators. So how am I suppose to determine which one will be less nucleophilic?


texts:
I know this kind of question has been asked many times but I think this is a bit different.

We have $G = H - TS$. Here I am talking about chemical reactions at constant pressure and temperature. We can write $\Delta G = Q - Q_\mathrm{rev} = \Delta H - T \Delta S$.

For an irreversible chemical reaction, for example an exothermic one, if $q = -10~\mathrm{kJ~mol^{-1}}$ (exothermic), then $Q_\mathrm{rev}$ could be $-9$, $-8$, $-7$, etc.  The difference $(Q – Q_\mathrm{rev})$ would be negative ($-1$, $-2$, $-3$, etc.).  This represents the portion of $Q$ that can be converted into non-PV work.  The remainder of the heat is dispersed into the surrounding and is wasted. Right?

So here $Q$ as absolute value is more than $Q_\mathrm{rev}$, so we have more heat generated than a reversible chemical reaction that can be used as work ($Q = 8~\mathrm{kJ~mol^{-1}}$ and $Q_\mathrm{rev} = 2~\mathrm{kJ~mol^{-1}}$). So why is it said that a reversible reaction produces more useful heat? Again, I am talking about chemical reaction and not mechanical process.


texts: Why is the benzyne triple bond distorted?

texts:
In many places I've seen the "extra" bond in benzyne being labelled as $\ce{sp^2-sp^2}$ overlap or distorted (not parallel) $\ce{p\pi-p\pi}$ overlap. But I've failed to see why we can't have a normal, parallel $\ce{p\pi-p\pi}$ overlap.

Wikipedia says:

  In benzyne, however, the p orbitals are distorted to accommodate the triple bond within the ring system, reducing their effective overlap.

That makes no sense to me — why can't a normal, parallel $\ce{p\pi-p\pi}$ overlap be "accommodated" within the system.

So, what is the reason for the distorted $\pi$ bond in benzyne?

I'm fine with answers involving a bit of QM/MO theory.


texts: Why are there two Hydrogen atoms on some periodic tables?

texts:
Most periodic tables only feature one Hydrogen atom, on the top of the first group. But some, like the one I was given, also show Hydrogen in the 7th group, to left of Helium.

Why are there two Hydrogen atoms? What's the difference between the two, and why do we work with the left one more often than the right?


texts: Molecule with reversible exothermic conformational change?

texts:
I proposed some exotic biochemistry on the Worldbuilding stack.
https://worldbuilding.stackexchange.com/questions/166814/digestive-system-of-the-ultimate-omnivore/166829#166829

  Your creature oxidizes molecules in its "stomach" which is more of a
  furnace. Anything that can be oxidized is fair game - any reduced
  carbon, or nitrogen, or metal salt. Oxidation produces heat. The
  amount of heat produced is controlled by controlling oxygen ingress to
  the stomach.

  Under hot conditions, certain metalloproteins change configuration.
  The circulation brings these proteins into hot conditions near the
  stomach and they capture heat energy with the configuration change.
  When the hot-configured metalloprotein circulates out to the cold
  exterior (possibly radiator plates or fins) it shifts back to the cold
  configuration. This conformational shift is linked to an ATPase and
  generates ATP for the creature to use for its muscles and metabolic
  processes, as Earth life does.

I was challenged to produce a molecule which could capture and release energy in this way. Molecules do this all the time with a phase change - that is a steam engine. But is there any example of a molecule (or a whole type, perhaps) which undergoes a conformational change with heat that it later discharges in a controlled manner, with an exothermic relaxation back to the cold conformation. Not necessarily a biomolecule.


texts:
So I have been trying to understand how to draw R and S configurations. I feel like I have understood how to draw them, but every time I do a question, I get a wrong answer.

So here is what I have understood,

The lowest priority goes to the back of the compound meaning on the dash line.
The highest priority is on the top.
You can play around with the 3rd and 4rth, so that one is on the
'out of page' and the other is on the line, so that you can
differentiate between the R and S.

But then there is this picture for example from my book,

I have been going crazy trying to understand it. The things I do not understand are these,

1) I understand the diagrams on the right side. That I have been doing as well

2) But then when we look at the diagrams on the left. The configuration is completely opposite. Even though it says S, the configuration is like of a R. Plus the highest one is going into the page and not the hydrogen. WHY? It is driving me crazy because they do that for all the examples. When they S, they actually make an R and vice versa. Whereas on the internet it is a different story. So I really need someone to tell me what I should do.


texts: Reaction of vicinal diol in presence of benzaldehyde

texts:
Could someone please help me figure out the products of the following reaction?

Here are few possibilities I've come up with:

The attacking reagent could the given vicinal diol, with its nucleophilic lone pair, attacking the electrophilic carbon of benzaldehyde. However, that doesn't seem to lead me anywhere.
As the reaction is carried out in acidic medium, one of the -OH groups (or both?) could be protonated, to become better leaving groups leading to formation of a carbocation intermediate. What after that?

Chances are it's probably a nucleophilic addition, proceeding through a tetrahedral intermediate, than a carbocationic one.

It'd be great if someone could show a proper mechanism for the reaction, and explain why it should be so. Thanks a lot!


texts: Are there any good examples of commonly ingested molecules that contain particular toxic individual elements?

texts:
In the house on my own and an article popped up on my feed with the following statement:

  While the Government has insisted the chemical is safe, cadmium is
  recognised as a cause of lung cancer and during the Second World War
  was considered by the Allies as a chemical weapon.

The proceeding paragraphs are about zinc cadmium sulphide.

full article

I think this is a flawed argument, essentially inferring that any given molecule can be said to be toxic just because one of it's component parts is toxic but I can't think of a good example to back this up.

What is a good example of a common compound that is ingested often (daily?) but contains a particularly toxic element if that element were ingested in some way on it's own?


texts: What are possible hazards of fog machines?

texts:
From a chemistry point of view I would like to learn about possible hazards of fog machines.

Such devices, also called “foggers”, create vapor which appears like fog or smoke. It is used in discos, parties, etc.
It works by heating “fog juices” which are made of glycerine and distilled/de-ionized water mix or propylene glycol and distilled water mix.
I don't know the temperature these mixes are heated by the machines.

I know glycerine and propylene glycol are not hazardous, but I would like to know if heating them can pose any risk. I've talked with someone who works in this industry and he couldn't tell if there has been any study to show if the fog produced by these foggers is harmful or not.
So even though these devices have existed for years I would still like to know if they can be harmful and if they should be avoided when possible.

How you can help as chemist is by telling me if vaporizing glycerine and distilled water mix at certain temperature can cause any change to the supposedly harmful substance and make it dangerous or not.


texts: According to Wikipedia, HF is miscible with water. But isn't hydrogen fluoride a gas at RT and a sensible pressure? What would happen if you just kept adding more HF gas to some water?


texts: Deviation of real gases from ideal behaviour

texts:
From the Amagat's curve we can see two types of result for real gases.

If we increase pressure,the value of $PV$ decreases initially and then the value starts increasing for the gases like- carbon dioxide, nitrogen, oxygen, methane, etc..
If we increase pressure,the value of $PV$ starts increasing initially for the gases like - hydrogen, helium, etc.

Now please explain what're the reasons behind this kinda behaviour of real gases?


texts: I'm stuck with this problem. If I have 200 grams of a solution at 30% how much water should I add so that the concentration becomes 25%?


texts:
This excellent answer describes the appearance of solvated electrons in ammonia as first a blue, and then metallic color. It is produced by dissolving sodium in ammonia at low temperature. According to Wikipedia this is called an electride:

An electride is an ionic compound in which an electron is the anion. Solutions of alkali metals in ammonia are electride salts. In the case of sodium, these blue solutions consist of $\ce{[Na(NH3)6]+}$ and solvated electrons:
$$\ce{Na + 6 NH3 → [Na(NH3)6]+e−}$$
The cation $\ce{[Na(NH3)6]+}$ is an octahedral coordination complex.

Question: How to interpret the shape in this representation of an electride?
Included in the Wikipedia article is the image shown below. Is it fairly self-evident to chemists what this image represents? If so could someone help me understand it? I see little things which might represent the location of solvated electrons, and a larger continuous/contiguous? surface which might represent all of the ions and molecules and the fact that any moment most of them are in some degree of bonding with each other, but that's just my guess. What defines the surface, some sort of threshold on electron density?
In this case the original source might be hard to track down, so an "educated guess" by someone familliar with this kind of representation would be welcome.
I'd like to read more about this kind of 3D representation of an ionic solution, so an introductory source would be appreciated.

below: "Cavities and channels in an electride", from here.


texts:
I am having a bit of trouble understanding variations to rate equation problems.
What I know:

For $\ce{A + B -> AB}$, if the rate is proportional to the concentration of A and B, the rate equation is:

$\quad$ rate=$\ce{k*[A]^1*[B]^1}$

For $\ce{A + A -> 2B + C}$, if the rate  proportional to $\ce{[A]}$:-

$\quad$ rate=$\ce{k*[A]}$ , as per  Question 1c and Answer 1c.

Question 1 : Why is this the case?
E.g. when it was $\ce{1A + 1B}$ and the rate was proportional to the concentration of $\ce{A}$ and $\ce{B}$ our rate equation contains $\ce{[A]*[B]}$. But for $\ce{1A + 1A}$ why does the rate equation contain $\ce{[A]}$ instead of $\ce{[A]*[A]}$?
Question 2: Do molecules change anything (compared to single atoms)
Is $\ce{A + A}$ equivalent to $\ce{A2}$
E.g. will all of these have the same rate equation (if the rate is proportional to $\ce{[A]}$)

$\ce{A + A -> 2B + C}$
$\ce{A2 -> 2B + C}$
$\ce{2A -> 2B + C}$

I can't see why they wouldn't all have the same rate equation as it would just be different ways to represent the same total $\ce{[A]}$.


texts: Physical Meaning of the Difference between MO and VB Wave Function of H2?

texts: What would be the physical meaning of the difference between the MO wave function and VB wave function of $\ce{H2}$?


texts: Explain why the noble gas Kr does follow the general trend for covalent radii

texts:
Looking at covalent radii I know the trend states that as you move from LEFT to RIGHT the radii decreases due to increased nuclear charge. Up until you hit the noble gasses like neon. Neon does not want to form a covalent bond with itself so we have to look at the van der Waal forces to determine its radii (which is bigger than Fluorine, disproving the trend).

Up until you reach Krypton, the noble gasses tend to be slightly larger than the halogen group.

I am having a hard time understanding why the noble gas Kr does follow the general trend for covalent radii in the fourth period, even though the noble gas Ne does not.

Would it be because of the greater shielding effect?

Covalent Radii of 2nd Period and 4th Period Halogen and Noble Gase.

F
 - 0.064 nm

Ne
 - 0.070 nm

Br
 - 0.114 nm

Kr
 - 0.109 nm


texts:
I think that the first reaction would add into the ketone carbon, but I don't know where to go after that.
A step-by-step explanation of the answer would be greatly appreciated!

Answer choices:


texts: How to calculate concentrations and what is the concept of 'mole'?

texts: Say I have a $50~\mathrm{ml}$ solution of a liquid mixture which is $30~\%$ concentrated. Now if I take $20~\mathrm{ml}$ of that liquid out from that mix, what would be the resulting concentration of both the liquid remaining and the liquid extracted? Will the concentration of both still be $30~\%$?


texts: How important are those fields of chemistry in biotechnology and medicinal chemistry

texts:
At my university there is some fields of chemistry that i don't know if i should focus on them...

How important are in biotechnology and medicinal chemistry those fields of chemistry? :

Quantum chemistry
Physical chemistry
Computional chemistry


texts: How do I have to interpret the input to the OCC flag in Molpro?

texts:
I'm trying to understand the occupied orbital specification in Molpro. They're specified by the OCC flag, while it's stated in the documentation, that

OCC, m1, m2, ..., mn;

where the mᵢ are the number of occupied orbitals (including core/frozen and closed).

Let's say I want to compute energies in $\ce{N2}$, which has $D_\mathrm{2h}$ symmetry point group, i.e. the following character table:
$$D_\mathrm{2h}\\
\begin{array}{ccc} \hline
\text{No.} & \text{Name} & \text{Function}\\
1& \mathrm{A_g}    & s  \\
2& \mathrm{B_{3u}} & x  \\
3& \mathrm{B_{2u}} & y  \\
4& \mathrm{B_{1g}} & xy \\
5& \mathrm{B_{1u}} & z \\
6& \mathrm{B_{2g}} & xz \\
7& \mathrm{B_{3g}} & yz \\
8& \mathrm{A_u}    & xyz \\
\hline
\end{array}
$$

Then, what exactly does the OCC specification in the following code mean?

{hf-scf;
 occ,3,1,1,0,2,0,0,0;
 wf,14,1,0;
}

In my understanding, it specifies:

3 orbitals of $\mathrm{A_g}$ symmetry, i.e. $s$ orbitals
1 orbital of $\mathrm{B_{3u}}$ symmetry, i.e. $p_x$ orbital
1 orbital of $\mathrm{B_{2u}}$ symmetry, i.e. $p_y$ orbital
2 orbitals of $\mathrm{B_{1u}}$ symmetry, i.e. $z$ orbital

What I find strange with this interpretation is the choice of orbitals - why would I choose 3 $s$ orbitals, while only one $p_x$ and 2 $p_z$?


texts: In adsorption, the concentration of adsorbate is greater on the surface. So, how is it possible that the solvent will be more on the surface and the solute (adsorbate) in the bulk… or does solute not always mean adsorbate?


texts: What gas law is involved when your ears "pop" when you are on a plane high in the air?

texts: When you are up in the air, the air pressure decreases and the altitude increases. What gas law is involved in the situation wherein your ears "pop" because of the difference in pressure.


texts: What is the advance of OFET's (Organic Field effect transistors) over the traditional CMOS Transistors?


texts: What is the configuration of dimethyl[tris(trifluoromethyl)]-λ⁵-phosphane?

texts:
I know that $\ce{(CH3)2P(CF3)3}$ is geometry of trigonal bipyramid and according to Bent's rule $\ce{CH3}$  goes to axial positions and $\ce{CF3}$s remains on equatorial positions. However, as per Bent's rule more electronegative ligand goes to axial position.

Now my question is how to determine which is more electronegative between $\ce{CH3}$ and $\ce{CF3}$?


texts:
It is said that 4-methylbenzoic acid will be a weaker acid than benzoic acid. 4-nitrobenzoic acid will be a stronger acid than benzoic acid.

I don't understand why the methyl group on 4-methylbenzoic acid would affect the acidity. I know that it has an inductive effect (hyperconjugation) but I thought induction only had an effect over a one to two carbon distance. The carboxylic acid is separated from the methyl group by four carbons.


texts: Is ruthenium really invulnerable to aqua regia?

texts:
Recently, I answered a question "What metals aren't dissolved in/attacked by aqua regia?" in which I finally concluded "ruthenium is resistant to aqua regia in any form at any concentration of acid".Fellow answerer  @Linear Christmas also supported my statement

However, in my answer, I pointed out that something is not right. In the blockquote I wrote:

  Ruthenium can be dissolved in aqua regia only when in the presence of oxygen (Why? will be asked in a separate question)

It is written that ruthenium can only be attacked in aqua regia in the presence of oxygen. And for this statement, this question is asked. This statement can also be found in the wikipedia article of noble metal.

In the wikipedia article of ruthenium it is clearly written that:

  Ruthenium (...) is not attacked by acids (even aqua regia)

Even in the handbook, it is written that (statement can be found in my answer):

  Ruthenium is by far the most chemically resistant of the noble metal,
  unattacked either in hot or cold aqua regia.

Also this video by Nurdrage shows that ruthenium is invulnerable to aqua regia or any kind of acid.

However in this google book, it is written:

  Pure ruthenium powder or sponge is not appreciable attacked by hot, single or mixed mineral acid(aqua regia).

Why it is written "not appreciable attacked"? Maybe it should have wrote invulnerable or resistant. I am assuming that the corrosion rate is not appreciable/very slow i.e. corrosion is too slow to get noticed by naked eye.

Is my assumption correct? Can ruthenium be attacked in aqua regia only in presence of oxygen? Why wikipedia wrote that statement regardless of the fact that ruthenium is resistant to aqua regia in any form at any concentration of acid? I have not found any evidence that shows ruthenium is vulnerable to aqua regia.