texts: Is (cycloprop-2-en-1-ylidene)propanedinitrile aromatic or not?

texts: Is (cycloprop-2-en-1-ylidene)propanedinitrile ((cycloprop-2-en-1-ylidene)malononitrile) aromatic or not? If yes? How?


texts: Difference between change in energy level and hyperfine energy level?

texts:
The second is the duration of 9 192 631 770 periods of the radiation
  corresponding to the transition between the two hyperfine levels of the
  ground state of the cesium 133 atom.

  --> This definition refers to a cesium atom at rest at a temperature of 0 K.

-From what I learnt, changing in energy level of atoms means change from the ground state to the "excited" state. Does "transition between the two hyperfine levels" as quoted above has the same meaning?


texts: How many boiling points does a mixture of liquids have?

texts: Let's say I have a mixture of two miscible liquids. I want to get the liquids by fractional/pure distillation. My textbook says a mixture boils over a range of temperatures. On the contrary, another book I read says a mixture has only one boiling point and that the liquid with a lower boiling point adds more of itself to the mixture. I am wondering which of those is correct and will work with distillation.


texts: Steam Distillation - Condensate not going through condenser

texts:
Basically what the title says.  I set my equipment up exactly like pretty much every diagram I could find.  There's condensation through the claisen adapter and into the distillation adapter, but for some reason, the condensation won't fall slide down into the condenser tube.

The boiler flask has been at a roaring boil for several hours, the water going through the condenser tube is hooked up properly and ice cold, and the receiving flask is sitting in ice.  Everything is identical to the diagram.  I've tried it with and without the thermometer - and with and without the separatory funnel but the condensate won't get in the consdenser tube.

Any ideas?


texts: How to analyze a acid and salt mixture using titrimetry?

texts:
Given a mixture of $\ce{HCl}$ and $\ce{MCl3}$ and the following dissociation constants for $\ce{M(OH)3}$, how can the concentrations of $\ce{HCl}$ and $\ce{MCl3}$ be determined separately by titrating this solution with a standard strong base (say, $0.1\:\mathrm{M}$ $\ce{NaOH}$) ? I want to be able to sketch the approximate titration curve for this titration too.

\begin{align}
\ce{ M(OH)3 &~<=> M(OH)^{+}_{2} + OH^{-} } &
\mathrm{p}K_{\mathrm{b}1} &= 0.5 \\
\ce{ M(OH)^{+}_{2} &~<=> M(OH)^{2+} + OH^{-} } &
 \mathrm{p}K_{\mathrm{b}2} &= 0.7 \\
\ce{ M(OH)^{2+} &~<=> M^{3+} + OH^{-} } &
 \mathrm{p}K_{\mathrm{b}3} &= 9.0
\end{align}

All of the species in above equilibria are water soluble.

Progress so far:

$\ce{HCl}$ in the medium will first react with the base and give rise to an end point.
As $\ce{MCl3}$ is a salt of weak base and a strong acid (i.e. $\ce{M(OH)3}$ and $ \ce{HCl} $), a solution of $\ce{MCl3}$ is acidic due to the following equilibria (hydrolysis reactions).

\begin{align}
\ce{ M^{3+} + {H2O} &~<=> M(OH)^{2+} + H+ } &
\mathrm{p}K_{\mathrm{a}1} &= 14.0 - 9.0 = 5.0 \tag{a} \\
\ce{ M(OH)^{2+} + {H2O} &~<=> M(OH)^{+}_{2} + H+ } &
\mathrm{p}K_{\mathrm{a}2} &= 14.0 - 0.7 = 13.3 \tag{b}\\
\ce{ M(OH)^{+}_{2} + {H2O} &~<=> M(OH)_3 + H+ } &
\mathrm{p}K_{\mathrm{a}3} &= 14.0 - 0.5 = 13.5 \tag{c}
\end{align}

Therefore, if further $\ce{NaOH}$ is added, $\ce{H+}$ generated by above equilibria will react with that $\ce{NaOH}$.
Looking at the $\mathrm{p}K_\mathrm{a}$ values of $\mathrm{(b)}$ and $\mathrm{(c)}$ it can be assumed that reaction $\mathrm{(a)}$ is the dominant of the three. And it will give rise to a separate end point.

Now the problem is how to put all these information together and deduce a method to analyze the mixture.

Any help on how to sketch the titration curve, choose indicators and practically carry out the analysis would be greatly appreciated.


texts: Which acid to choose when designing a world with acid seas?

texts:
I'm currently writing a narrative and hoping to include a world which is home to a sea of some form of 'nasty' substance (doesn't have to be acid).

The varieties of inhabitants of this world have evolved mostly on the lands and eventually built their cities right up to the shorelines of this acidic sea. (In some cases I may even have cities that float and migrate across it).

I'm imagining some kind of scientific or industrial endeavor they perform whereby they've created ships that can withstand the chemicals (at least in short term) by lining their hulls with a type of ablative shielding.

Also desirable (although not essential) would be for the composition to not be immediately fatal. A carbon life form (or would they likely be silicate?) could fall in and maybe swim for a few minutes and leave with only some semi minor chemical burns. Yet prolonged exposure would most definitely be fatal.

I'm also wondering if the inhabitants could harness this chemical in some imaginative way such as for propulsion or agricultural/industrial means?

My question is, what kind of chemical/cocktail could I use to fit these kinds of parameters?


texts: Iron(III) nitrate and hydrogen peroxide reaction

texts: When iron(III) nitrate is added to hydrogen peroxide as a catalyst, the temperature initially decreases and begins to increase after 30 seconds. Why is this the case? (is there any intermediate reactions of $\ce{H2O2}$ and $\ce{Fe(NO3)3}?)$


texts: Conditions for choosing quantifying and qualifying ion in LC-MS/MS

texts:
In my PhD-work, we are trying to develop LC-MS/MS methods for targeted analysis. Usually, I determine my quantifying ion/fragment based on a few different criteria:

If there is a 13C internal standard of identical structure, stick with the same fragment for both.
If not, look for the lowest noise/highest area/lowest LOD
If two fragments are similar in the previous manner, I have a look if there are different levels of contamination in the method blanks

For most compounds, that works, but for a small subset I have the case where the method blanks are similar, but for the fragment with the lowest LOD, noise is highest and/or areas are lowest between the two fragments we analyze for.

Would you go for the fragment with the highest area, highest noise (assuming a large number is more robust against small changes) and the highest LOD, or the lowest one? Is there a best practice I can refer to? There is a 1-2 order of magnitude difference between the LODs, so I really don't want to misrepresent the data.

Thanks in advance!


texts: Is it possible to compute the colour of *any* molecule?

texts:
Above are some spectral emission lines for hydrogen, helium and neon.

Using the Schroedinger equation, it's possible to derive the colours that hydrogen will emit when light is fired at it. A little more complicated (although beyond my rudimentary knowledge of quantum mechanics), the same can be done for helium, and so on.

Of course as we progress to molecules, even the relatively small $C_5H_{11}Br$, it's (I'm told) very hard to predict the colours emitted from first principles, and even then incorrect assumptions must be made (like the Born-Oppenheimer approximation), so upon progressing to larger molecules, we find that these simplifications diverge from experiment.

My question is this: with the advent of computers, are we able to (in practice, not theoretically in a few decades) accurately compute the colours given off by a molecule  by numerically solving the laws of quantum mechanics for complicated systems? Much like nonlinear differential equations can now be 'solved' with computers without any simplifying assumptions (like $\sin(x) \approx x$), is it in humanity's capacity today to approximate colours from first principles, so that computing time is the only restraint? Note the difference between an incorrect model of reality (Born-Oppenheimer), and one that converges to the correct one (even if slowly).


texts: Why is ice sticky between −20 to −8 degrees Celsius but not below −30 °C?

texts:
I was watching an Air crash investigation video where the cause of the plane crash was determined to be due to blockage of fuel pipes by ice crystals (from the water in the jet fuel) which would have formed while the plane was cruising over Siberia where temperatures are as low as −74 °C. Now the engines were working fine until the fuel temp. was −30 °C. But as soon as it started getting warmer near London, Heathrow and the fuel temp hit −20 °C the ice crystals coalesced to form a mesh that completely blocked the fuel pipes and caused the engines to lose power and end up crashing.

My Question is: What caused the ice to not stick at a colder temp (−30 °C) when I believe the molecules would be vibrating slower than those at −20 °C? It seemed from the investigation's experiment that below −20 °C big ice crystals don't form at all, if they do they're tiny. So why does the increase in temperature help ice sticking?


texts: What is the difference between lead tetraacetate and sodium periodate as reagents?

texts:
I recently came across this question which has confused me about the  usage of $\ce{Pb(OAc)4}$ and $\ce{NaIO4}$ reagent.
Both the reagents have nearly the same cyclization mechanism, but the answer to this problem says that $\ce{Pb(OAc)4}$ should be used for the conversion instead of $\ce{NaIO4}$.
The first thing that I noticed was that, the compound is a trans-1,2-diol, so $\ce{NaIO4}$ might not be the appropriate reagent, but I could not understand how $\ce{Pb(OAc)4}$ is appropriate for this conversation .
Please suggest the essential difference between these reagents.


texts:
I have been struggling hard for writing IUPAC naming of this compound.

Anhydride with benzene having five membered ring can be named as benzene dicarboxylic anhydride and five membered ring without benzene can be named as pentane -1,5-dioic anhydride. But what can I do for this compound?


texts: Why is ionization energy measured in gaseous phase?

texts:
When I looked up the definition of ionization energy, it says:-

  it is the energy required to remove one electron from the shell to
  infinity in an atom in gaseous state.

Why is it measured in gaseous phase and not in any other phase?


texts: Atomic coordinates for DNA bases as they appear in a B-form or A-form duplex

texts: Where can I find atomic coordinates for guanosine / cytosine / thymine / adenine (either the ribonucleotide or deoxyribonucleotide bases) where the atoms are configured in the manner we would expect in the context of an idealized B-form or A-form nucleic acid duplex?  I'd like to calculate the angle between various bonds in these bases, and to play around with a few other things, but I'm having trouble finding proper atomic coordinate sets.


texts: Can bridged and bridgehead positions be chlorinated using free radical mechanism?

texts:
When the above compound is treated with $\ce{Cl2}$ in the presence of sunlight ($h\nu$), what is the number of monochloro structural isomers formed?

I expected only 1 product becuase I don't believe that monochlorination can take place at the bridgehead or the bridge positions. And rest of the 4 positions, by symmetry, are equivalent. This is because chlorination takes place through free radical mechanism in which a $\ce{sp^2}$ hybridised carbon free radical is formed.
But the answer given in the test's answer key is $3$. I think they have considered the products of bridgehead and bridged positions too but I don't understand how that is possible.


texts: How can two same reactions have a different reduction potential

texts: According to wikipedia the reduction of AgCl (s) to give Ag (s) and $Cl^-$ (aq) has reduction potential of 0.22 V . But it also says tha the reduction of $Ag^+$ (aq) to give Ag (s) has reduction potential of 0.80 V . In the former reaction the oxidation state of +1 and gets reduced to zero oxidation state and chloride acts as spectator ion whereas the same happens in the latter reaction just without the chloride ion. Also I believe silver chloride is a strong electrolyte and dissociates completely. So my question is If both the reactions are exactly identical then why isn't there reduction potential same ? I am super confused, any help will be highly appreciated.


texts: Number of atomic and molecular orbitals in different Hartree-Fock references

texts:
For a given molecule and electronic configuration,

Are the number of contracted atomic orbitals (AOs) different in a restricted open-shell Hartree-Fock (ROHF) calculation from an RHF calculation? What about unrestricted Hartree-Fock (UHF)?
Are the number of molecular orbitals (MOs) different in a ROHF calculation from an RHF calculation? What about UHF?

For example, if we are using the STO-3G basis set for a water molecule, we get 1 + 1 + 5 = 7 contracted functions for AOs in an RHF calculation, leading to 7 MOs. Are any of these numbers different in an ROHF calculation? What about UHF?

Essentially, what are the core differences between AOs and MOs within each approach?

For water molecule using sto-3g basis I obtained the orbitals in the following order For RHF: Occupied (A1) (A1) (B2) (A1) (B1) Virtual (A1) (B2) For ROHF: Occupied (A1) (A1) (B2) (A1) (B1) Virtual (A1) (B2) But if we take alcohols for an e.g., the number of such orbitals is not the same. I want to know how they are calculated, so that atleast I could do them by hand. For the RHF one, it is nicely explained in "Modern Quantum chemistry" by Szabo-Ostlund. I want some similar information on ROHF and UHF (if possible).


texts:
I know both HDPE and PP have at least some degree of resistance to aldehydes, esters and aliphatic hydrocarbons.
I am concerned however about minute contamination over time of pure samples and so I wonder how PP and HDPE compare to each other as to their resistance to aldehydes (mainly) as well as to the other two groups.


texts: Will PAEK polymers hydrolyze in concentrated sulfuric acid?

texts:
One of my duties at the company where I work is to perform intrinsic viscosity (IV) experiments on PAEK (poly(aryl ether ketone)) polymers. These polymers don't dissolve well in most solvents, so the solvent for these experiments is concentrated sulfuric acid. I've found that if I leave the mixture to dissolve overnight and/or at too high of a temperature, the resulting IV is much lower (approximately half) than if I run the experiment as soon as all the material has dissolved at lower temperatures. The PAEK compounds I'm referencing are ones like PEK, PEEK, and PEKK (the results I've detailed above were seen primarily, maybe exclusively, with PEKK). The structures for these polymers is below.

PEK:

PEEK:

PEKK:

My thought on this was that with extra time and heat, the water in the sulfuric acid could attack the carbon alpha to the ether oxygen, hydrolyzing the polymer and creating shorter chain lengths. One of my colleagues disagrees, but to be honest, I haven't asked her to explain why.

Aromatic sulfonation can also occur when PAEK polymers are dissolved in concentrated sulfuric acid, as documented here, but I wouldn't expect that to have such a large impact on the viscosity (and I would also expect the effect of sulfonic acids to increase viscosity, not decrease it, though I'm less confident about that). My background is organic chemistry, not polymer chemistry/materials science, so I'm not super familiar with how different aspects affect things like viscosity. I do know shorter chains leads to a lower viscosity, though.

So here's my question: Is it likely that a significant amount of hydrolysis is occuring, or is it more likely some other factor causing this effect?


texts: Can assumptions made during calculation of ka of buffer solutions be justified?

texts:
We make many assumptions in sciences which are not always true but as they make little difference we ignore them for simplicity. But today I have decided that I can no longer be lured into using expression of $K_{a}$ and $K_{w}$ by assumptions which I deem to make a significant difference.

We say that $[H_{2}O]$ is constant. Why I think it is not justified?
$$\ce{H2O + HCL <=> H3O+ + Cl-}$$
$[H_{2}O]$ is almost $ 55.6 \:\mathrm{mol\:dm^-3}{}$.
At around $20^{o}C$ $20\:\mathrm{mol}$ of $HCl_{aq}$ can be dissolved. Let's say we dissolve $20 \:\mathrm{mol}$ of $HCl$ and try to find it's WE ASSUME that % disassociation of water is $100 \%$. So we must take $[HCl]\approx0$ that means that $20\:\mathrm{mol}$ of $H_{2}O$ has reacted and $[H_{2}O]$ is no longer a constant but has rather changed to $35.6\mathrm{mol}$.
So this expression can no longer be used. $$K_{a}=\frac{[H_{3}O^{+}].[Cl^{-}]} {[HCl]}=K_{c}.[H_{2}O]$$
Note: you might point out that $K_{a}$ is not used for strong acids but I just used $HCl$ as an example but make my point easier to explain.
Assumption made about concentrations when calculating $Ka$ of buffer solutions.
$$CH_{3}COOH_{aq} \rightleftharpoons CH_{3}COO^{-}_{aq} + H^{+}_{aq}$$
We have added $CH_{3}COONa$  to make a buffer solution.
$$CH_{3}COONa_{aq} \rightarrow CH_{3}COO^{-}_{aq} + Na^{+}_{aq}$$
So,
$$[CH_{3}COO^{-}]_{total}=[CH_{3}COO^{-}]_{CH_{3}COONa} + [CH_{3}COO^{-}]_{CH_{3}COOH}$$
$$[CH_{3}COO^{-}]_{CH_{3}COOH} = [H^{+}_{aq}]$$
BUT WE ASSUME that $[CH_{3}COO^{-}]_{total}=[CH_{3}COO^{-}]_{CH_{3}COONa}$ because we say $[CH_{3}COO^{-}]_{CH_{3}COOH}$ is negligible yet we include [$H_{aq}^{+}]$ in the expression which has same value as $[CH_{3}COO^{-}]_{CH_{3}COOH}$. Same value is considered negligible at one place and not negligible at another in the same expression. How is that justified?


texts:
Ethyl glucuronide (EtG) is formed by conjugation with glucuronic acid catalyzed by the enzyme UDP-glucuronosyltransferase.

My question: Is it possible for EtG to form spontaneously in a urine sample that contains a small amount of ethanol?


texts: How big is the influence of basis set and functional on ZPE and thermal corrections?

texts:
Most quantum chemistry packages are capable of computing ZPE and thermal corrections for a given temperature. But how big is the influence of the basis set chosen and the functional used?

Is it sufficient to calculate this at a lower level than the corresponding final high-level single point calculation? What about differences between the energies - if there is an error, is it systematic so that energy differences are not affected?


texts:
In my 12th standard book, the formula for entropy change is given as $\Delta S = \frac{q_\text{reversible}}{T}$. What is the importance of absorbing heat reversibly and not irreversibly? What does absorbing heat reversibly mean? Does it mean that the process should be reversible, and if it does, then how would we define change in entropy of a spontaneous process i.e an irreversible process?
 Would its formula also include $q_\text{reversible}$?


texts: Galvanic corrosion: Copper, iron and aluminum in an automotive cooling system

texts: I am building a small copper heat exchanger I am going to plumb into my coolant system. I'm afraid that the copper will corrode my aluminum radiator or iron engine through galvanic action via the coolant. How was this prevented on older vehicles with iron engines and copper radiators? Or is this less of a problem then I expect it will be?


texts: Which d-orbitals split according to CFT?

texts:
According to CFT, the degenerate d-orbitals split into $eg$ and $t_2 g$ groups. Are these the outermost nd orbitals which are vacant(4-d in case of 4th period) or the penultimate filled (n-1)d orbitals?

If they are the (n-1)d orbitals, how can they be degenerate if they are not completely filled? If they are (vacant) nd orbitals, how do they split into $eg$ and $t_2 g$ groups if they have no electrons to be repelled by the incoming ligands (CFT is based purely on electrostatic forces)?


texts: What chemicals cause the acrid smell of burning food?

texts: When roasting vegetables in a oven, after a while there is a nice caramel smell. After that, if they start burning, there is a smokey smell, and if they continue to burn, the smokey smell gets more and more acrid. The smell really sticks in the back of your throat/sinuses, and induces gagging if it's strong enough. What chemicals make up the gasses and particles that cause that acrid smell?


texts: How to test for fluoride levels in drinking water?

texts:
I would like to test for fluoride levels in the water.

Are there any methods or test kits available to test the levels of fluoride in home water supply?

See also: Is there any at home test for fluoride levels in your water, and what is the best water distillation unit?


texts:
If increasing/decreasing the concentration of an excess reactant influenced the percentage yield of a product experimentally, how could this be explained?

I know that in theory, the excess shouldn't affect the yield- since it's the limiting that decides how much is produced. But is there any possible explanation for this result?


texts:
I've recently found out my calculated value of internal energy of methane largely deviates from the ab initio output (at $\pu{1000 K}$ $0.058~\text{Hartree} = \pu{152.3 kJ mol-1}$). I used HF method, I know it's not highly-accurate, but I just need what internal energy should roughly be.

The way how I calculate:

$$H = U + PV = U + Nk_\mathrm{B}T$$

where $U$ is the internal energy, $H$ is the enthalpy.
In this case, $\Delta_\mathrm{f}H = \pu{-74.9 kJ mol-1}$ (I found the enthalpy value of methane from heat of formation table on Wikipedia).

So, I simply substitute the temperature $T = \pu{1000 K}$ into the equation and I got $\pu{-83.2 kJ mol-1}$. First, the internal energy of a system cannot be negative. Second, even it's positive, why it deviates that much from ab initio calculations? Can someone give me a hint?


texts: Rate of exothermic/endothermic reactions

texts: Is it necessary that all endothermic reactions be slow and all exothermic reactions fast? This is based on the fact that endothermic reactions require more activation energy than exothermic reactions to initiate a chemical reaction. Or  are there some endothermic reactions that can be fast without the presence of a catalyst?


texts:
I have began to do an "art project" which utilizes solder as main material.

While I know that solder is cheap and easily found in multiple shops, I have set my mind on using recycled solder from out of use PCB's.

I've recovered a somewhat pure amount of material by using solder suckers, but a significant amount is trapped in my DIY desoldering braid which is simply salvaged wires. Those wires might be copper or some grey wires salvaged from a PC power supply.

What I have been able to come with is:

Some video I watched used (IIRC) $\ce{HCl}$ to dissolve solder from PCB's. My main issue is that I can't easily procure high concentration $\ce{HCl}$. My second issue is the acid reacting with the copper and maybe rendering the solder not usable (if this turns out to be a non-issue, I could figure a way to procure the acid).
I have been thinking of pulverizing the solder covered wires using a coffee grinder then heating the powder to the meting point of the solder, mechanically separating the two.

I wanted to ask if any of the two ways above would work without specialized equipment, or if there was a third way.


texts:
I am confused about Positive behaviour from ideal behaviour as to why it occurs.

1) Molecular attractions plays a dominant role in positive deviation

OR
2) Molecular volume plays dominant role in positive deviation

I am confused these two facts.


texts: Acidic strength order of mineral acids in acetic acid

texts:
Explain this acidic strength order $\ce{H2SO4} > \ce{HCl} > \ce{HNO3}$ in acetic acid.

My Attempt

Stability of conjugate base is proportional to the acidic strength of acids in acetic acid.

$\ce{SO4^2-}$ has two resonance structures.
$\ce{NO3-}$ has three resonance structures.
$\ce{Cl-}$ is stable due to octet formation.

As for electronegativity order, Cl is on par with N (almost equal).

According to stability, $\ce{HNO3}$ must me more acidic than $\ce{HCl}.$ Also, electronegativity of N & Cl is almost the same.

So, according to me, the order must be $\ce{HNO3} > \ce{H2SO4} > \ce{HCl}.$

Where am I wrong? Please explain.


texts:
From Wikipedia-1, and from an answer here on Stack-Exchange, I can list at least the following elements which will dissolve in aqueous $\ce{NH4OH}$:

$\ce{Cr(III), Co(III), Ni(II), Cu(I, II), Zn(II), Ag(I),}$ along with  "several platinum group metals"

From reading Wikipedia-2, I also suspect the following elements to dissolve in liquid ammonia:

$\ce{Mg, Ca, Sr, Ba, Eu, Yb, Li, Na, K}$ and $\ce{Rb}$

As a matter of fact, according to Wikipedia "almost all metal ions bind ammonia as a ligand." I thought it would be interesting, and potentially very useful, to find out which metal ions are NOT soluble in $\ce{NH4OH}$.

I can list two for now:

$\ce{Fe(OH)3}$
$\ce{Mg(OH)2}$ with a solubility product of only $5.61×10^{−12}$ (credit to Oscar Lanzi)


texts: Melting points and boiling points of primary alcohols do not follow the same trend

texts:
If one considers boiling points (in °C) of primary alcohols, one finds the following:

methanol: 65
ethanol: 79
1-propanol: 97
1-butanol: 117
1-pentanol: 138

This trend is due to Van der Waals forces increasing with molecular weight.

Now if one focuses on melting points, I would expect the same trend, but these are the experimental values (in °C):

methanol: −98
ethanol: −117
1-propanol: −127
1-butanol: −90
1-pentanol: −79

the lowest value being the melting point of 1-propanol.

The general idea stating that with all else being equal, more massive molecules have higher boiling and melting points, does not fully apply for this set of alcohols.

So my question: why melting and boiling points of primary alcohols do not follow the same trend?


texts: I do a fair bit of biochemistry, and one of the things I've taken on faith up until now is that ATP is stable because it has a high kinetic barrier for falling apart despite the spontaneity of its decomposition. I understand that it does, but what about the transition state of ATP hydrolysis in an aqueous solution is so high energy? For that matter, what is the transition state of spontaneous ATP hydrolysis?


texts: Further reading on photoconductivity of hemoglobin

texts: I recently ran into this paper which describe experiments that confirm that hemoglobin is photoconductive. Finding this fact as incredible, I wanted to read up more on photoconductive properties of hemoglobin. The paper does not discuss what the conductivity number is, that would give some estimate of charge carrier density created when hemoglobin is illuminated. Do you have any estimates of how conductive hemoglobin gets? Is it close to highly doped semiconductors? Also, if you can provide links to papers that discuss more on photoconductivity of hemoglobin, that would be appreciated, as Google only showed me this sole paper from 1963.


texts: Is there a difference between equilibrium and steady state?

texts: The term equilibrium is used in the context of reversible reactions that reach a point where concentrations no longer change. The term steady-state is used in enzyme kinetics when the concentration of the enzyme-substrate complex no longer changes (or hardly changes, in case of a quasi steady state). It is also used to describe multi-step biochemical pathways. Is there a difference between the two, given that both concern a situation where concentrations don't change over time?


texts: How is elimination reaction (E1) possible without base and in presence of acid?

texts:
When learning about E1 we were taught that three things are important factors to judge if the reaction is E1 or E2

Substrate ( 3,2,1 favours E2 but only 3 favours E1 )
Base ( Stronger Base favours E2 , weaker Base disfavours E2 hence suggests E1 ) But E1 requires a base however weak
Leaving group ( E1 is more sensitive to LG because it initiates E1 ) Bad LG disfavours both , excellent LG favours E1 more

This was from David M Kleins Book " Organic Chemistry I as a Second Language "
But in Section 11.6 he says this

fact, the reverse path (starting from the alcohol and ending with the alkene) is a reaction that we have already studied. It is just an E1 reaction

Then he goes on to show this picture

Initial question : How do you have an elimination reaction without a base, that too in the presence of an acid ?
(Although I understand that E1 's rate doesnt depend on a Base but it is still needed)
Answer : there is a Base ( H20) which makes it look very much like E1 .
Edit : it behaves very much like an E1 but with an extra step
Step 0: converts the bad LG to an excellent LG
Step 1: LG leaves
Step 2 : Base abstracts proton to make alkene
New question:  Why does water behave like a base in an acidic mixture? And why does it not react with the H+ already in the solution ?


texts: Is it OK to dispose of potassium hydrogen phthalate into the sewer system?

texts:
I have been using potassium hydrogen phthalate (KHP) for creating primary standards. I have looked into the Flinn catalog, and the disposal consideration is classified as "organic acids, must be neutralized prior to drain disposal." That seems easy enough, but with recent publications of health concerns of phthalate exposure I just want to make sure. I have looked everywhere, and I can't find any additional information as to how this stuff can be disposed.
I know some of you use this in your labs. How do you dispose of it? I could reduce it down in solution or hire a company to take it away, but if it's safe to neutralize and empty into the sewers I'd rather save the time and money.
Thanks in advance for any help!


texts:
I was reading about chemicals that control pore size of polyurethane foams and there it was mentioned that "tensides" decrease pore size. What are tensides? I assume it's the opposite of a surfactant, that is, it increases surface tension, but that is just my guess. I have no idea what it actually is.

I tried to Google it but strangely I just got bunch of "surfactant" results even through I wrote it just tensides. Some German site when translated from German to English changed the word tenside to surfactant, so I don't know if it is different class of chemicals or just a German word for surfactant. From the original article where I saw the word, it was written in a way as to suggest that they both are different from each other.


texts: Why there is an exception in melting and boiling point in p block?

texts:
Why is the boiling point and melting point of 15th group and 16th group has an exception?

We know that as molecular mass increases boiling point and melting point also increase. So, down the group 15 and 16, as molecular mass increases, melting and boiling point should also increase but melting and boiling point of antimony is more than that of bismuth. (even though molecular mass of bismuth is more)

Similarly, melting and boiling point of tellurium is higher than polonium. Why is it so?


texts: What is the best way to calculate the mass percentage of Calcium Carbonate from water?

texts:
Where I live it's believed that local tap water is really bad for drinking because of the amount of limestone. As a science experiment for school I wanted to approximately calculate the percentage of calcium carbonate in tap water so I can make the conclusion: Is that amount of drinking $\ce{CaCO3}$ actually the problem or something else?

This question might be similar to DK4's question but I'm trying just to calculate not extract, only by using items you can find in a typical house (or in a local shopping center).

If calcium carbonate isn't the issue what is?

Edit: As pointed out in comments, percentage of $\ce{Mg}$ is also applied.


texts: At what voltage does the electrodeposition of the metal start?

texts:
The question is as follows:

  An aqueous solution containing each of $\ce{Au^{+3}, Cu^{+2}, Ag^{+}\;and\;Li^{+}}$ ions each at the concentration of $1 \mathrm M$, is being electrolysed using inert electrodes. The value of the standard potentials are:
  $$E^{\circ}_{\ce{Ag^{+}|Ag}}=0.80\,\text{V} = E_1 \\
E^{\circ}_{\ce{Cu^{+2}|Cu}}=0.34\,\text{V} = E_2 \\
E^{\circ}_{\ce{Au^{+3}|Au}}=1.50\,\text{V} = E_3 \\
E^{\circ}_{\ce{Li^{+}|Li}}=-3.03\,\text{V} \\ $$
  With increasing voltage, the sequence of deposition of metals on the cathode will be:

  Ans: $\ce{Au, Ag, Cu}$

I understand with the increasing value of the standard reduction potential (SRP), the tendency of the metal to get reduced increases, and so obviously, the metal with the highest SRP is deposited first. So we get the increasing order as the answer. But, when I tried to justify this by trying to calculate the specific voltages when electrodeposition should start, I ran into some problems. What follows is my attempt at that. (The following part has been added to the question by me as an edit).

Let us assume we use a battery of $V$ volts, with the polarity as shown in the diagram. Edit 2: The $V$ here is the minimum voltage required for electrodeposition to start. Now, as the negative end of the battery supplies electrons, so the silver will deposit on that electrode, and so (using the comment by f") oxygen is evolved at the other electrode. We have the electrode reactions as:
$$\ce{O2 + 2H2O + 4e^- -> 4OH^-}\qquad E^\circ = V_1 = 0.401\,\mathrm{V}$$
$$\ce{Ag^+ + e^- -> Ag} \qquad E^\circ = V_2 = 0.80\,\mathrm{V}$$
So I reasoned as follows: the hydroxide ions are in the solution, and according to the equation (and its standard reduction potential), the solution is at a higher potential than the the "sink" of electrons, that is the anode. Similarly, the solution is at a lower potential compared to the source of electrons, that is the anode. As both $V_1$ and $V_2$ are positive, using Kirchhoff's Law, we have:
$$V+V_1+V_2=0$$
So here we have a contradiction. Both $V_1$ and $V_2$ are positive, but so should be $V$, because of our explicit assumption of how the terminals are connected. But this equation tells us that $V$ is negative!

So what is wrong with this line of reasoning?

Thank you.


texts:
I made some "super" soap bubbles with my kids using the following ingredients:

liquid dish soap
tap water
corn syrup

We left the solution out over night last night here in Maine and the temperature got down to −3 °C. This morning we found that the solution left in the lid had grown a vertical icicle.

There is no trickery here. I stepped outside and found these items as you see them below.

How could this icicle have formed?


texts: What element has good conductivity but is also brittle?

texts:
I'm confused by what element(s) can be identified to have these properties.

The following is text from my 2019-2020 Kaplan MCAT General Chemistry book under the metalloids section

  Silicon (Si) has a metallic luster but is brittle and a poor conductor

So onto the MCAT Concept Check 2.2:

  Identify a few elements that  likely possess the following  properties

  Good conductivity but brittle

I flip to the answer key and it says:

  Metalloids exhibit brittleness but good conductivity

So I'm confused how this makes sense because Si was the main example they provided in that passage, and it seems to contrast the two points they make.

So what is an actual example of good conductivity but brittle??


texts:
How can you make an unfavorable reaction go backwards?

From my understanding if we wanted a reaction at equilibrium to go backwards (i.e. form reactants from products), we would add more product into the solution.

But I'm not sure how the reaction being an unfavorable one changes the above statement.

After making the reaction go backwards, we have changed the reaction rate going backwards correct?


texts: Why do some diagrams of some molecules show the bonds of only some of their submolecules?

texts: In the diagram of ATP below this paragraph there are no lines between the atoms in the $\ce{NH2}$ molecule or in the $\ce{OH}$ molecules; however, there are lines between all the other atoms. Does the omission of those lines represent some facts about  $\ce{NH2}$ and $\ce{OH}$ in the ATP molecule, or did the illustrator omit them in order to emphasize the rest of the molecule?


texts:
How do I draw a double Newman projection for cyclohexane? Which bond(s) do I sight down?

From what I understand, if we have 1-methylcyclohexane, we sight C1-C2 and C5-C4, as shown in my attempt below:

Would this be correct? I wish to achieve level 4!


texts: How to prepare a solution of accurate concentration?

texts:
How does one accurately dose powders? I would like to know what tools are used and how.

For example, how would one apply 1 gram of a certain powder to a solution in a beaker? Specifically, how do you make sure all of your measured powder (or at least with a very small error margin), gets into the solution, without too much of the powder sticking to the spoon or other utensil.

I figured one might dip a spoon loaded with the powder in the solution, but then the solution might stick to the spoon.


texts: Find pH and Kw for water with given values of conductivity

texts:
At $\pu{25 ^\circ C}$, $\lambda_\infty (\ce{H+}) = \pu{3.5 \times 10^{-2} S m2 mol-1}$ and $\lambda_\infty (\ce{OH-}) = \pu{2 \times 10^{-2} S m2 mol-1}$. Determine $\mathrm{pH}$ and $K_\mathrm{w}$.

Given: Specific conductance $= \pu{5.5 \times 10^{-6} Sm-1}$ for $\ce{H2O}$

My Attempt:

I know I need to find the concentration of $\ce{H+}$ or $\ce{OH-}$ for $\mathrm{pH}$. $K_\mathrm{w}$ can be found subsequently. However, I have no clue as to how do I find that with the given information.

I am also aware of the relation between conductivity, Specific conductance, and molarity. It is easy to find the molarity from the given information, but that would be of no use as we need the concentration of the individual ions rather than the molarity of the solution.

Any help would be appreciated.


texts: Hybridization state of oxygen in carbonyl sulfide (COS)

texts:
I've been scratching my head on this one for awhile here. In a carbonyl sulfide (COS) molecule, what is the hybridization state of oxygen?
Carbonyl sulfide is composed of a single carbon atom double bonded to oxygen and sulfur atoms. The sulfur and oxygen atoms each harbor two lone pairs.

Looking at oxygen, I count electron-dense groups:

There is one bonded atom
There are two lone pairs

This should amount to an sp2 hybridized orbitals for oxygen, before exceptions are accounted for.
Checking if any lone pairs are delocalized:

Oxygen both participates in a pi-bond and is adjacent to a carbon that participates in a pi-bond

This is where I'm stuck. Are any of oxygen's lone electron pairs delocalized due to these facts? Is the hybridized orbital not sp2 for oxygen?


texts: Intuition of following the lowest curvature mode to find a saddle point on a PES

texts:
In this paper A dimer method for finding saddle points on high dimensional potential surfaces using only first derivatives, it is mentioned that

  The saddle point is a maximum along the lowest curvature mode.

The curvature in this paper refers to the second derivate of the PES.

I know that mathematically, a saddle point minimizes the PES in all but one direction, and it is the highest point on the minimum energy path (MEP). But this cannot help me understand why the saddle point is a maximum along the lowest curvature mode.


texts: How to find volume needed from a stock solution

texts: I am making a media that is amended with substrates after being autoclaved in order to keep the media anaerobic. In order to do this, we make stocks of the solutions from a known concentration. I am having trouble figuring out what amount of liquid to add to one liter. For example, I make a 100 ml stock of sodium fumarate (160.04 g/mol) using 0.6402 grams in 100 ml of MQ H20. The final desired concentration in the liter media is 40 mM. How do I figure out how much of the liquid stock of sodium fumarate I am supposed to add? Thanks in advance for the help!


texts:
For the above molecule, I know that the longest carbon chain has 7 carbons, so the backbone is heptane.

The two substituents are at the 4 position on the heptane.

One of the substituents is a methyl group. That much is obvious.

The other appears to be a complex substituent and is a 1-chloroethyl group.

Thus, would the name be:

4,4-(1-chloroethyl)methylheptane?

I think the issue is what happens when we have different substituents with the same loctant. I've looked in one book and at all its practice problems, and this scenario never occurs.

I know that 4-methylheptane is a real compound and that its name is correct. So I am leaning toward 4,4-(1-chloroethyl)methylheptane as being a correct name; the complex substituent is correctly named; both locatants are present; everything is alphabetized; my only issue is whether I am missing some convention (e.g. should there be a dash somewhere, a comma somewhere, or what?)


texts: In wave physics, when waves interact, the principle of superposition applies. It states that the displacement of the resultant wave is made up of the sum of the individual displacements of the interacting waves. This appears to be very similar to the expression of a molecular orbital $\psi$ as a sum of the different atomic orbitals $\psi_i$ with different weighted coefficients. Is there any overlap between the quantum chemical basis of LCAO and superposition of waves?


texts:
Today, I had a friendly debate with my friend on what should be the oxidation state of $\ce {Cl}$ in the chlorine monoxide radical. I took the view that it should be $\ce {+2}$ while he took the view that it should be $\ce {+1}$. My reason for taking this view is simply that conventional state rules tell us that $\ce {O}$ should have a $\ce {-2}$ oxidation state assigned to it, when it is not part of a peroxide or in the superoxide ion, and when its bonding partner is less electronegative than it. His reason, on the other hand, is that one of the Lewis structures that can be drawn of this radical, features a $\ce {Cl-O}$ single bond. Hence, considering this single bond to be an ionic bond, we would thus observe charge separation to produce $\ce {Cl^+}$ and $\ce {O^-}$.

I would think that his perspective of the issue is flawed. Firstly, it is because there is more than one way of representing the covalent bonding between the two atoms. In fact, a simplistic MO diagram would allow us to deduce a bond order of $\ce {+1.5}$. Furthermore, a Lewis structure with a $\ce {Cl=O}$ double bond can also be drawn, although with $\ce {Cl}$ carrying a total of nine electrons. Hence, I believe that the approach of assigning states based on one's interpretation of the covalent bonding between the two atoms is inaccurate in this case. By following the conventional oxidation states, there would thus be no ambiguity in the assigning of oxidation states in this case.

Which view do you think is correct and why?


texts:
I was wondering about molecular orbitals of methylene different states 1B1 3B1 1A1
and how are they connected to symmetry point group lower case 1a1, etc orbitals what those numbers and alphabets mean?

It would be great if someone can derive those orbitals from symmetry and show me which states 1B1, 3B1 and 1A1 are referred to and what does up script, subscripts and alphabets stand for and connect them to lower case 1a1 ,etc.


texts: Can hydrofluoric acid etch glass at a pH of 7.0?

texts:
Will it still etch glass when very dilute? Will the reaction still proceed slowly? At what pH will the reaction stop completely?

From Wikipedia on hydrogen fluoride: "Although hydrofluoric acid is regarded as a weak acid, it is very corrosive, even attacking glass when hydrated."
On hydrofuoric acid: It etches glass "by reacting with silicon dioxide to form gaseous or water-soluble silicon fluorides. "

It seems fishtank glass can be etched even when the water is kept at a pH of 7.0.
"You might try a razor scraper, to see if that will remove any of it. If not, there is a very high chance they are due to etching. Etching is caused by the action of water, especially acidic water, over a long period of time. "


texts:
I am going to prepare tert-butyl protected threonine. I was going for the classic esterification methodology which is acid catalyzed (sulfuric acid) esterification under reflux of tert butyl alcohol + threonine. My worry is that the -OH r group of threonine will also be esterified. My lab has very few reagents. We don't have TMSCI, silicone, amberlyst or carbodiimide. Does any of you have any suggested methods using tert butyl alcohol?

Thank you!


texts: How exactly do we superimpose molecules while checking optical activity?

texts:
I am struggling with these type of questions where in some cases we rotate a molecule's mirror image by 180 degrees to check superimposability.

Like when checking any tetrahedral chiral compound, we draw its mirror image and rotate it by 180 degrees and say that it's not superimposable.
Suppose the mirror image of the left-handed version is the right-handed version, hence both are not superimposable. If we rotate the right-handed version by 180 degrees and then try to check, will it be superimposable now? Similarly, trans 1,2 dimethyl cyclopentane is chiral but if we rotate its mirror image by 180, is it superimposable?


texts: Why some hydrates are coloured while other are not

texts:
I was studying about different vitriol and noticed that some hydrates are coloured while some are colourless even after having water in their crystals.

For example; $\ce{FeSO4.7H2O}$ (iron sulfate heptahydrate) has a green colour while anhydrous iron sulfate has no colour, similarly $\ce{CuSO4.5H2O}$ (copper sulfate pentahydrate) has a blue colour while anhydrous copper sulate has no colour. When we come to zinc sulfate,it has no colour in all of its three hydrates (the most common one being the heptahydrate).

Why does zinc sulfate not have any colour like $\ce{FeSO4.7H2O}$ or $\ce{CuSO4.5H2O}$ regardless of whether it has water of crystallisation?


texts:
It was recently brought to my attention that my understanding of entropy is wonky at best.
In my experience, entropy was introduced (superficially at best) during general chemistry/foundations of inorganic chem and described in terms of order/disorder of a system, usually followed by some messy room analogy. In one of my textbooks, the author, Gary Wulfsberg, was discussing how a reaction tends to favor the products "if it increases the dispersal of ions/molecules over a larger volume of space..."(Wulfsberg, G., 2018). Wulfsberg goes on to say that

The measure of this dispersal or disorder is known as the entropy (S) of the substance. A
positive entropy change for a reaction indicates increasing dispersal or disorder
(Wulfsberg, G., Foundations of Inorganic Chemistry; ch. 4, pg. 200)

which I interpreted it as him saying that all systems that increase in entropy have a corresponding increase in disorder.
Later in my undergraduate career, Boltzmann's entropy was introduced during thermodynamics and described by my professor as the amount of micro-states available for the particles within the system and that an increase in entropy corresponds to an increase in the states that the system can exist in.
All was fine and peachy until recently, when I came across an article that discusses the Shannon Measure of Information (SMI) and entropy. In an article by Arieh Ben-Naim, he talks about how the idea of order/disorder in relation to entropy is not necessarily correct, in fact it is a fallacy that does not hold true nor can order/disorder be measured definitely for all systems. He states,

It is true that many spontaneous processes may be viewed as proceeding from an ordered to a disordered state. However, there are two difficulties with this interpretation. First, the concept of order is not well-defined, and in many processes it is difficult, if not impossible, to decide which of the two states of the system is more or less ordered.
J. Chem. Educ. 2011, 88 (5), 594–596

Additionally, he talks about how some systems do have "order parameters", however, it is not in relation to entropy and that not every process where an increase in entropy is observed has a corresponding increase in disorder. He later goes on to describe the SMI treatment of entropy "as the number of binary questions one needs to ask to find the location of the particle." Hence, if the number of yes/no questions one needs to ask to find the location of particle increases, so has the thermodynamic entropy.
So here is my question
Is entropy described by Boltzmann/statistical mechanics the same as the entropy described by Shannon information theory?
Additionally, is there any validity in relating order/disorder in describing the change in entropy of chemical systems?


texts: If a chemical formula for a mineral contains a comma, are there limits on the amounts of each element?

texts:
I have a chemical formula for the mineral actinolite which is: $$\rm{Ca}_2({Mg,Fe})_5{Si}_8{O}_{22}({OH})_2$$

The formula contains a "," which I understand means that the magnesium and the iron can have different combinations (up to 5 total).

The question is, if magnesium is the dominant atom, is it possible for the amount of magnesium to be less than iron and still be actinolite, or must magnesium always have the greatest amount?


texts: What does "lit." mean in boiling point or melting point specification?

texts:
For example, this Xanthene 99% specification from Sigma Aldrich states:

\begin{array} \\\hline
\text{bp}  & 310-312 ~^\circ\mathrm{C~ (lit.)} \\\hline
\text{mp}  & 101-102 ~^\circ\mathrm{C~ (lit.)} \\\hline
\end{array}

My guess is that it's from literature.


texts: What are the effects of storing drinking water in a copper container?

texts:
I recently learned that Ayurveda recommends storing drinking water in copper containers for positive health benefits.

Upon my simple experimentation, I've noticed the following effects:

Water Type : activated carbon filtered drinking water

Duration of storage: 8 hours

The taste of the water changed, it tasted more metallic. I think this is because of the increase of dissolved copper in the water.

If I'm drinking 4-5 liters of water per day, would that be still under the safe limit of 2 mg/day? ref 2 Note: I don't have any apparatus to measure the copper content in the water.

I've researched a bit and found that it does have some positive effects on killing some microbes such as bacteria ref 1. Note: I'm not able to deduce any conclusion about the increase in copper content from this paper even though the author said it is "within the permissible limits."

I would like to know more about the studies related to this claim and I'm really interested to know about the side effects.


texts:
I have learned hybridisation as a concept created to explain the same $\ce{C-H}$ bond lengths in $\ce{CH4}$.

I found it easy to find the type of hybridisation in different molecules, but my problem is how to find whether an atom in a molecule under goes hybridisation or not.

For example, $\ce{N}$ goes under hybridisation in $\ce{NH3}$, but there are some examples where $\ce{N}$ won't hybridise (not sure abt $\ce{N2}$, if you may suggest). In $\ce{ClF3}$, $\ce{Cl}$ is hybridised but in $\ce{PCl5}$ $\ce{Cl}$ is not.

I want the reason for undergoing hybridisation.


texts: What is an algorithm for drawing resonance structures?

texts:
Question

What is an instance of a procedure for writing resonance structures for any given compound's name or structural formula?

I would prefer any of these formats to represent the algorithm:

Numbered list
Flow diagram
Pseudocode

Any format that is human-readable and has ordinated the steps is probably okay.

Purpose

For myself, I would like to have such an algorithm because I prefer to systematically solve problems. I may also wish to write a computer program to perform this task in the future, so understanding the logic in more detail would help me create the decision tree.

For others that do not understand how to draw resonance structures, I hope the responses to this question are useful for their learning. I've seen a lot of people struggle with this topic.

Demonstration of Effort

I have been combing through my organic chemistry textbook (Organic Chemistry, Seventh Edition, L.G. Wade, Jr., Whitman College, Pearson, Copyright 2010) for rules to drawing resonance structures.

Here are the general principles I have found:

Each resonance structure has the property of being a valid Lewis structure
Electrons can be delocalized
Nuclei cannot be delocalized (ie don't move them)
Prefer placing pairs of electrons to instead of single electrons
Never separate pairs of electrons
Maximize the number of octets acheived among the atoms that obey the octet rule
Maximize the number of bonds in the structure
Prefer to place negative charges on electronegative atoms
Prefer to produce structures with minimized charge separation
Prefer structures with a negative formal charge instead of positive formal charge


texts:
How can we justify the longer length of the dative bond by bridge Cl with Al?
Is it because to prevent steric hindrance or repulsions the Cl atom is farther away from other Al as compared to normal Cl?


texts: Why does ethene react explosively with fluorine?

texts:
In this website it is claimed that "[e]thene reacts explosively with fluorine to give carbon and hydrogen fluoride gas", via this equation:

$$\ce{CH2=CH2 + 2F2 -> 2C + 4HF}$$

Why does the fluorine hog the hydrogen atom instead of attacking the $\pi$-bond?

Additionally, may I ask for the mechanism of this reaction?


texts: What is the significance of enthalpy definition not under constant pressure?

texts: Under constant pressure (and only PV work), change in enthalpy can be shown to equal change in heat. If enthalpy is not meaningful outside of constant pressure, then why not use heat instead? So I think it must be meaningful outside of constant pressure scenarios, but I couldn't figure it out myself. Can someone help?


texts: What goes on the NFPA 704 for multiple chemicals?

texts: If you have a chemical that is classified (Health, Fire, Reactivity) 2, 1, 2. And another chemical that is 1, 3, 2. If these two chemicals are stored together, what is put on the storage container/building? What is the rule for this; the largest in each category is displayed, 2, 3, 2. And the specific hazards are listed?


texts: Extract all structures of Gaussian 09 molecular dynamics calculation using babel?


texts: Why doesn't copper react with hydrochloric acid while the other metals do?

texts:
5) Which one of the following metals does not react with hydrochloric acid?

  A. zinc
  B. magnesium
  C. iron
  D. copper
  E. aluminium

The right answer must be copper, but why doesn't copper react with hydrochloric acid while the other metals do?


texts: How can we measure the atomic radius of an atom?

texts:
The definition of atomic radius is half the average internuclear distance of an atom.

But many times I've been told that it is not possible to handle a single atom. Thus how can we measure the internuclear distance of an atom?


texts: melting and boiling ...really equilibrium?

texts: Why are melting and boiling considered equilibrium processes even though the amount (concentration)  of both phases keep changing i.e from solid to liquid and so on?


texts: Chromium +1 is unknown while Mn+2 is known?

texts: Although both $\ce{Cr+}$ and $\ce{Mn^2+}$ both ions have $d^5$ configuration, still only $\ce{Mn^2+}$  is well-known while $\ce{Cr+}$ is not common. What is so special about Cr that it does not form $\ce{Cr+}$?


texts: Combustion of NaCl(aq) when testing conductivity

texts: In a experiment that dealt with electric conduction of many concentrated solutions, NaCl(s) created an unknown, to me, substance after adding a drop or two of water. Furthermore, it isn't the reaction of water and NaCl(s) that I don't understand, but the reaction between the anode and cathode when they came in contact with NaCl(aq), sparks were present and it seemed to have "burned" NaCl(s). The question is: what is the correct name for the part that "burnt"?


texts: Activation Energy in Acid/Base reactions

texts:
For simple acid/base reactions - i.e. those involving inorganic compounds - does activation energy ever play in reactions?

Or can we ignore kinetics entirely and just consider thermodynamic factors such as conjugate stability?

I'd be very interested if there were some book or article examining inorganic molecules' acid-base behavior from a kinetic standpoint.


texts: Calculate voltage, cost and time of nickel coating

texts:
To nickel with a bath of $\ce{NiSO4}$ a cathodic current of $\pu{0.3 A/cm2}$ is applied with a square plate of side $\pu{5 cm}$ is used to nickel a certain substrate. Due to the formation of $\ce{H2}$ the current efficiency is $75\%.$ If the resistance of the solution is $\pu{0.4 \Omega}$ and the price of the current $\pu{1 c€/kWh},$ determine the voltage to be applied, the energy cost and the
  required time to nickel a total surface of $\pu{2 m2}$ with a coating thickness of $\pu{0.03 cm}.$
  Data: $M(\ce{Ni}) = \pu{58.71 g/mol}$; $\delta(\ce{Ni}) = \pu{8.9 g/cm3}.$

First I’m going to show you what I got

I’m sure this is wrong because I didn’t use given data. But I don’t know where should I use mass of nickel.

I’ve never seen this type of exercise before and I don’t where should I start from.


texts: Unique identifier for chemical substances?

texts:
One famous database for chemical substances is PubChem. If one reads the section about other identifiers than the PubChem ID for Ethanol one gets several CAS numbers (potentially deprecated ones as well), potentially several European Community (EC) Numbers and a lot of other identifiers which seem to be not really unique.

Is there a true unique identifier for chemical substances reasonable to be used in a database?


texts: How to calculate the pH of a 0.325 M solution of pyridine hydrofloride?

texts:
How to calculate the $\mathrm{pH}$ of a $0.325~\mathrm{M}$ solution of $\ce{C5H5NHF}$? The $K_\mathrm{b}$ for $\ce{C5H5N}$ and $\ce{C5H5NH+}$ is $1.7\times 10^{-9}$.

Here's my work, but it's wrong (at least I tried):

$$\ce{C5H5NHF -> C5H5NH+ + F- }$$
$$K_\mathrm{a}(\ce{HF})= 4.0\cdot10^{-4}$$
$$K=\frac{K_\mathrm{w}}{K_\mathrm{a}}$$
$$K=\frac{1\cdot10^{-14}}{4.0\cdot10^{-4}}=2.5\cdot10^{-11}$$

Construct an ice table:

$$
\begin{array}{|c|c|c|c|}\hline
&\ce{F-}&\ce{+H2O(l)->}&\ce{HF}&+\ce{OH-}\\\hline
\text{I}&\pu{0.325M}&&0&0 \\\hline
\text{C}&-x&&x&x\\\hline
\text{E}&\pu{0.325M}-x&&x&x\\\hline
\end{array}
$$

Set up the equation (small x-approximation):
$$2.5\cdot10^{-11} = \frac{x^2}{0.325-x}$$
Now, cross multiply:
$$x^2 = 5.87\cdot10^{-12}$$
Take the square root of both sides:
$$[\ce{OH-}] = x = 2.42\cdot10^{-6}$$
You want to get from $[\ce{OH-}]$ to $\mathrm{pOH}$:
$$\mathrm{pOH} = -\log\left(2.42\cdot10^{-6}\right) = 5.616$$
Then, from $\mathrm{pOH}$ to $\mathrm{pH}$:
$$\mathrm{pH} = 14 - 5.616 = 8.384$$
Which is the wrong answer.

What am I doing wrong? How do I even use the $K_\mathrm{b}$ value in my calculation?


texts: I have come across many reactions that are zero order reactions but at one glance I'm unable to tell if they are zero order or not.  Is there any criteria that can be used to identify these reactions or are they purely experimentally determined?


texts: What measures of the dielectric constant mark whether the solution is ionic, polar and nonpolar?

texts: At what numerical values of ε, then what organic compounds if any mark these thresholds.  How is that only for a vacuum has ε=1?  This is absolute lowest limit?


texts: Can an amide nitrogen be a hydrogen bond acceptor?

texts: Can $\ce{N}$ (i.e. main chain $\ce{NH}$s of recognised residues in a peptide or protein) be a hydrogen bond acceptor? It is a well known fact that the main chain $\ce{NH}$s can be a hydrogen bond donor (as observed in the α-helix), but can they act as a hydrogen bond acceptor? If yes, help me with an example or even better a reference. And, if no, why can't they act as an acceptor, after all it's an electronegative atom?


texts:
I always have trouble naming my graphs in class. They never seem too scientific or professional.

For example, we are reviewing density now, and had to graph the mass (Y) of different volumes (X) of water. So, very simply, my title was "Mass of Different Volumes of Water". Is this appropriate?

Are there any naming conventions, such as "X vs. Y", or "Effects of X on Y" or "Relationship of X and Y", etc.? Sorry if this is a bit stylistic and opinion based, but I would like some feedback. Thanks.

Note: I'm in the tenth grade.

Note 2: I'm also not sure what site to post this under (there's no "science" site) nor what tags to post this with. Feel free to improve it.


texts: Finding simplest formula of a compound with following specifications

texts:
I ran into the following problem, wherein I'm asked to find the simplest formula of a compound containing $50 \%$ of element $X$ (atomic wt. 10) and $50\%$ of element $Y$ (atomic wt. 20).

I know about few laws of chemical combinations. I think Law of Definite Proportions may come into play.

$$\text{atomic wt. }X:\text{atomic wt. } Y=1:2\implies XY_2$$

Am I correct in my reasoning? If not kindly point out the flaws, if any? Thanks


texts: What is the reason for more stable keto form to tautomerise to a less stable enol form?

texts: In the mechanism of SeO2 I have seen that a more stable keto form first converts to a less stable enol form and then yields a diketone. I have seen many other reaction where the reactant converts to an unstable form first and then reacts. My doubt is why does the reactant converts itself rather than just simply not react ?


texts: Mechanism for interconversion of spin isomers of hydrogen

texts:
What is the mechanism by which the ortho- and para- spin isomers of hydrogen interconvert?

If such a mechanism exists, does this mean that ortho-hydrogen increases in concentration on increasing temperature?


texts: Am I limited by the pKa value of an weak acid when preparing a buffer solution of it (and its salt)?

texts:
If I was to make an acidic buffer system with the ph of, for instance, 4, would I be limited with my choice of weak acids? That is, how big does the difference between pH and pKa have to be in order for the weak acid not to be usable? Or is that not the case? I am very well aware that the optimal weak acid for has to have a pKa value quite close to the pH of the wanted buffer because they offer the most buffering capacity.
Also - Can someone hook me up with some equations applicable for making/dealing with buffers other than the Henderson Hasselbach equation? Are there any equations that can help me predict the buffer capacity?


texts: Acidic strength of diethyl malonate vs ethyl acetoacetate

texts:
Which would be more acidic, diethyl malonate $\left(\ce{CH2(CO2Et)2}\right)$ or ethyl acetoacetate $(\ce{CH3COCH2OOC2H5})$

In the above compounds, I have marked the hydrogen which I think will be the most acidic. Now removing that hydrogen would yield a carbocation. Both the carbocations would be equally stabilized due to resonance effect. In fact diethyl malonate acid would be more stabilized due to the extra inductive effect of the extra oxygen. Yet Wikipedia shows that ethyl acetoacetate has a p$K_\text{a}$ less than that of diethylmalonate acid.

What is making it more acidic?


texts: How can we do amide coupling reaction in water?

texts: Does anyone know if it is possible or if there are any protocols for amide coupling in water (and not a normal polar aprotic solvent like DMSO, DCM, ACN, etc.)?


texts: Improving copper contact and preventing oxidation

texts:
I have a model railway in which I use pure copper on the tracks and in the engine to power the train with electricity.

Is there any solution to prevent the copper surfaces from corrosion, and maybe improve the conductivity?


texts: Open Source SDF (Chemical Table File) Parser in any language

texts:
I'm looking to parse a large .sdf file and put it into a .csv file.

The only software I could find that parses .sdf files is OpenBabel's Pybel, but it won't properly install for my El Capitan, for either python2.7 or 3.+. (It's an open issue, and might hopefully be fixed with the next release). Are there any other languages/OSs that can easily parse this file?  If there aren't any, is there a recommended operating system I could spin up with VirtualBox that will easily run OpenBabel/Pybel?


texts: "Exactly Equal" and "At Least" in electron excitation

texts:
When we examine IR spectra, we see troughs corresponding to absorption at exactly a specific frequency that corresponds to the energy needed to stretch certain bonds (although translational motions and intermolcular forces can broaden the accepted frequency).

Coordination compounds absorb light at exactly the frequency corresponding to the crystal-field splitting energy.

However, when we talk about energy from photons required to break a  bond, we say "at least" the frequency instead of "exactly" in the examples above. Take $\ce{Cl-Cl}$ for example, we say that the photon must have at least a frequency of 607 THz (or wavelength of no more than 496 nm). There is still a definite energy involved here: 242 kJ/mol to promote an electron from a bonding MO in the molecule to an anti-bonding MO.

As another example, when we talk about ionizing radiation, we say that there is at least a certain amount of energy needed to ionize a compound. For example, my textbook says that a photon needs "at least 1216 kJ/mol" to ionize water. There is still a definite energy level involved: bringing the bonding electron from its negative potential energy MO to 0.

In all of these examples, definite energies were involved. Why is it that sometimes we say that that a photon needs to have exactly the energy needed, and other times the minimum energy needed?


texts:
In the hydrogenation of alkenes over a metal catalyst, the two hydrogen atoms are added with syn stereochemistry.

In the metal-catalysed dehydrogenation of alkanes, is the removal of hydrogen likewise concerted with syn stereochemistry? And if so, why?


texts: Degree of dissociation of acetic acid at infinite dilution

texts:
Afew drops of acetic acid are added to a large excess of water at $\pu{25 ^\circ C}$. In the limit of infinite dilution, what percentage of acid remains unionised? The $K_\mathrm{a}$ of acetic acid is $1.85\times10^{-5}$.

The answer is supposed to be 0.54%, but I'm not sure how to reach this value. I know that given the pH we can use the definition of $K_\mathrm{a}$ to calculate the ratio of $\ce{CH3COOH}$ to $\ce{CH3COO-}$, but how do I find the pH?


texts: Why is the concentration of protons equal to the concentration of a strong acid?

texts:
First, I know that strong acids are assumed to dissociate completely in water, so that the concentration of $\ce{H+}$ which they provide equals their concentration.

What I am asking for is not the concentration of $\ce{H+}$ which they provide, but $\ce{[H+]}$ for the solution, since the $\ce{H+}$ ions that they provide will not stay aloof, but rather will react with water and with $\ce{OH-}$ ions that are produced in the self-ionization of water.

Won't the reaction of $\ce{H+}$ ions with water shift the self-ionization of water
$$\ce{H2O <=> H+ + OH-}$$
to the left and won't their reaction with $\ce{OH-}$ shift it to the right according to Le Châtelier’s principle?

So, what will $\ce{[H+]}$ be for the solution?


texts: Hacking a pH meter and digital burette to partially automate a titration

texts:
This is a chemistry question about experimental techniques and technology.

I would like to connect a digital burette (Brand Titrette) and a pH meter to a computer and automate data acquisition to Excel. The pH meter would be connected to a platinum electrode with which I am measuring electrical potential during a titration. The objective is streamlined data collection to generate a titration curve (x-axis: volume, y-axis: potential) that would be used to identify the equivalence point of the titration.

Can anyone recommend an open source software that can be used to link excel to instruments?

Thank you,
Jeremy

Thank you,
JS


texts: Why is gauche conformer of 2,3 dimethyl butane more stable than its anti conformer?

texts:
Why is gauche conformer of 2,3-dimethylbutane seen along 2,3 bond more stable than its anti conformer? It seems to be anomalous to me as in most other butane like compunds anti form is more stable than gauche form.Can someone explain me the reason why the compound shows Gauche effect?

Also does this anomaly hold in case of 2,3-diphenylbutane and 2,3-dimethylpentane?


texts:
When (R)-2-bromobutane is heated with water, the $\mathrm{S_N1}$ substitution proceeds twice as fast as $\mathrm{S_N2}$. Calculate the appropriate enantiomeric excess and the specific rotation of the product of the mixture. The specific rotation of (R)-2-butanol is +13.5.

I din't understand how to interpret '$\mathrm{S_N1}$ proceeds twice as fast as $\mathrm{S_N2}$' mathematically.


texts: Determine balloon diameter needed to lift a 7 pound weight with various gases

texts:
My question is regarding setting up this equation. The givens are as follows:

Gases are helium, methane and hydrogen. (Test all three)
Assume balloon is spherical.
Assume temperature is $25~\mathrm{^\circ C}$

So I need to find the diameter of the balloon needed to lift a 7lb weight. I setup my equation as follows. $$m=\frac{PVM}{RT}$$

Next, I subtract my first gas ($\ce{He}$) from ambient air and convert my $m$ to equal grams in the weight. so I set it up like so.

$$3730.15~\mathrm{g}=\frac{PVM}{RT}-\frac{PVM}{RT}$$

Next I factor out the pressure and volume and fill in my numbers.
$$3730.15~\mathrm{g}=PV\left(\frac{(28.9~\mathrm{g~mol^{-1}})}{(0.0821~\mathrm{L~atm^{-1}mol^{-1}K^{-1}})(298~\mathrm{K})}-\frac{8~\mathrm{g~mol^{-1}}}{(0.0821~\mathrm{L~atm^{-1}mol^{-1}K^{-1}})(298~\mathrm{K})}\right)$$

This is where I am stuck at as I don't know what makes sense to use for pressure so I can solve for volume? Or maybe this is all setup wrong and makes no sense?


texts: Why is the electronegativity of potassium and rubidium same?

texts: The electronegativity of potassium and rubidium is reckoned at 0.82 for both. Why is it same for both of them? Shouldn't it be less for rubidium as compared to potassium owing to the addition of one extra shell in rubidium?


texts:
SO, I stumbled upon a periodic table of electronegativity-

http://www.thecatalyst.org/electabl.html

Now I don't understand why the first 3 noble gases have blank spaces instead of the electronegativities.

If it is because their octet is complete then why doesn't the noble gases Kr, Xe and Rn have blank spaces under them?


texts: Physical Explanation for variation of Gibbs Free Energy with Temperature and Pressure

texts:
Reading Atkins Elements of Physical Chemistry right now, and the book says:
"At constant pressure and entropy, an increase in temperature ($\Delta T\gt0$) results in a decrease in $G_\mathrm m$ (molar Gibbs energy) ($\Delta G_\mathrm m\lt0$)."
"At constant molar volume and temperature, an increase in pressure ($\Delta p >0$) results in an increase in molar Gibbs energy ($\Delta G_\mathrm m\gt0$)."

They have equations to describe this but I'm not really interested in the mathematical derivations (those are understandable) but rather in a logical, physical, and qualitative explanation of why these relations occur.

Given that $\Delta G$ indicates the maximum non-expansion work derivable from a system, what does this mean for the above relations? Does increasing the pressure of the system require work input ($\Delta G$ is positive) while increasing temperature result in the system doing work/an output of work ($\Delta G$ is negative)?

So, given a system (like a gas or something), why does $G$ change the way it does in response to $T$ and $p$ changes, and what does this physically mean for the system?

I'm a high school student (went through AP Chem) who's just trying to delve deeper into chemistry, so the simplest and most "layman's terms" explanation would probably help.


texts:
I read this in a textbook:

  $\ce{Bi(V)}$ is very unstable and is a good oxidizing agent.

Why does it happen that way? Is it because in $\pu{+5}$ oxidation state $\ce{Bi}$ pulls in more electrons and hence gets reduced fast or there's a different concept?

Also then $\ce{BiCl5}$ should be more stable than $\ce{BiCl3}$ because it's getting the electrons that it needs, which is not true.


texts:
As known, nitrogen could form 3 bonds based on octet rule, because it has 5 valence electrons. That means it needs 3 bonds.

On the other hand, why sometimes nitrogen forms 4 bonds?


texts: Calculate ozone layer thickness at a given temperature and pressure

texts:
The ozone concentration in the upper atmosphere averages $\pu{3.0 \times 10^13 molecules per cm3}$ in a region between $15$ and $\pu{35 km}$ high, at an average pressure of $\pu{0.001 atm}$ and temperature of $\pu{–25 °C}$. How thick would the ozone layer be, if these same molecules were at a pressure of $\pu{1.0 atm}$ and a temperature of $\pu{20 °C}$?

I understand that I need to use the ideal gas law, but I really have no idea how to approach the question, or even how to work with $\pu{molecules per cm3}$. I see that we have been given the values for temperature and pressure, but am unsure how to go about finding volume, and then the thickness.

I am also confused with how to deal with the two separate situations. Would you use $p = \pu{0.001 atm}$ or $p = \pu{1 atm}$. And would you use $T = \pu{248 K}$ or $T = \pu{293 K}$? And where do you find the value for the amount of substance?


texts: What happens when prop-2-en-1-ol reacts with concentrated hydrogen bromide

texts:
What happens when prop-2-en-1-ol (allyl alcohol) reacts with concentrated hydrogen bromide?

My Idea: I thought that in the first step protonation of the hydroxyl group will take place followed by formation of a carbocation. Then the attack of bromide ion from hydrogen bromide takes place and that would give me 3-bromoprop-1-ene. Also, I thought since the double bond still remains Markovnikov addition at the double bond might also take place.

But the reaction results into something different
Here is a picture of the above reaction:

The answer has been given as option C. Could someone point out where I might be going wrong or how should the reaction actually proceed?


texts: Clarification about the difference of internal energy formula

texts:
I am trying to understand the concept of internal energy and it's difference. My textbook said that the difference in internal energy of a system is

$$
\Delta U=Q+W
$$
where $Q$ is the heat absorbed or released by system and $W$ is the work done by system to the surrounding or by the surrounding to the system. After that, it mentioned that the signs of $W$ and $Q$ are determined like this:

  The work done by surrounding to system: $(+)$. The work done by system to surrounding: $(-)$. Same on heat.

After that general definitions, it started to explain the internal energy differences in various systems like isochoric system, isobaric system. In the section of isobaric system it says that:

  If a system were free that can expand against external pressure, when heat is given to that system, it will give some energy by doing some work. So the internal energy difference is:$$
\Delta U=Q_p-W
$$ where $Q_p$ is the heat given to a isobaric system.

It is completly OK till the new formula, but isn't the new formula bizarre? Because if we give heat to a system and it will do work. As a result the difference would be like:

$$
\Delta U_{example}=Q_{p_{example}}-(-W_{example})
$$
So, does the work done by system increase its internal energy?


texts: Balancing chemical systems - searching and sorting preliminary information

texts: I was hoping I could get help finding ways to sort information in the problem. What kind of information does "the conversion of toluene to benzene..." give us that is relevant towards solving the problem for values $R_G$ and $R_L$?


texts: The distinction between dynamic & static equilibrium

texts: How could we be sure that one certain reaction in equilibrium is dynamic? Since there would be no visible change in vessel, which property of the reaction would provide a proof besides color? Which laboratory technique could be used?


texts:
I am planning an experiment for a chemistry class about corrosion. I am going to show how different prevention methods affects the corrosion of iron and aluminium parts using bleach as the oxidizer.

One of the methods I plan on is protecting the parts using cathodic protection, the iron nail will be protected by aluminium but I don't know a good, easily available metal to protect the  aluminium stud. Any ideas?


texts:
Now at A, there is pressure by mercury column which is nothing but it's weight. Then, at C there is pressure which is atmospheric pressure. Also, the density at A is more than at C. What they say according to the law is that the pressure at C and A are same. I am not able to understand why the pressures are same actually because of the difference I listed in my text. Also, the pressure at C is inside the barometer and at A is outside. So, how can they ever be same and if they are, what is the condition for it.
Pressure at A = Pressure at B +pgh. Now how is this possible? Pressure at A should be more than pressure at B since the height for pressure at is more. So, why is that? Acceding to me Z it should be Pressure at A + pgh= pressure at B.
Then, they also say that pgh is atmospheric pressure. Where they used denstiy of mercury. Now, This should be mercury pressure and not atmospheric right. Density for atmosphere is very low right


texts: Why do distilled alcoholic beverages taste different from each other?

texts:
I was wondering about vodka vs. whiskey mostly. The way I understand it, a distilled beverage is created by heating a non-distilled beverage, say, beer, and then collecting and cooling the vapors.

Why would these vapors contain anything but alcohol and some water? Certainly the impurities that color, say, whiskey do not vaporize at the low temperatures involved? Why don't all distilled beverages taste and look like vodka (i.e. water and alcohol)?


texts: Why do we use phenolphthalein as an acid-base indicator?

texts: It seems that no resource I come across addresses the fact that the pH range for phenolphthalein's color change is around 8.2-10. In other words, it's still colorless at 8.2. Why then, is it claimed that the indicator changes colors when the solution changes from an acid to a base? Wouldn't you want an indicator that changes colors at about pH 7?


texts: How is "dietary cholesterol" processed in a human body?

texts:
Person eats an egg that is high in animal cholesterol ("dietary cholesterol").
What do chemical reactions play a role in breaking down it in stomach?


texts: How strict is the "to excite electrons the energy must equal the energy state difference" fact?

texts:
We are always told that to excite an electron from one state to a higher energy states, for example from the valance band to the conduction band, the energy must equal the energy difference between the two energy states.

The conduction band consists of many allowed energy states, separated from the valance band by an energy gap. For the element Si, this energy gap is (at room temperature) about 1,1 eV. The range of energies for visible light is 1.8 eV to 3.1 eV. Since Si indeed conducts electricity at room temperature, is it then assumed that there is an allowed energy states with exactly the same energy as the energy difference between the two states? The conduction band, or the valance band for that matter, is not continuous, but discrete. Or is it sufficient that the photon energy "roughly equals", or is "close enough"? If so, how close is close enough?

I hope my question is clearly stated.


texts: But what are anti-bonding pi-orbital? In search for an intuitive explanation

texts:
Imagine that you want to explain to an undergraduate why they have to to shade the pi-orbitals in a symmetrical way, i.e. dark on top (+), white on bottom (-) for two neighbouring pi-orbitals because they are bonding (or anti bonding), but then the student asks: why?!.. Can anyone  explain why this is without knowing about quantum mechanics and diving into molecular orbital theory? Intuitively, it makes no sense that an electron should 'care' why if they are 'on top' or 'on the bottom' of the nucleus.
I have a hard time both intuitively understanding, but also explaining why we care about bonding and anti-bonding orbitals. I know that I should draw them, and that one is stabilising while the other is destabilising. However, for a person with limited chemistry knowledge my reasons for why is simply:  'because it is so'. This is not very satisfying. I think this has something to do with the phase and wave equations (..etc) - but again,..this seems to go into heavy chemistry (..or?).
Question: Does someone have a nice analogy, or way of explaining why this is - and what anti-bonding orbitals are without any very high-level chemistry concepts?
I think there are others struggling with this concepts, as I found a few questions here on stack exchange that failed to give a satisfying answer. This might be because the concept is extremely complexes and not possible to understand without quantum mechanics... but thats why I want to ask the question here in hope of an intuitive explanation.
The linked questions:

Anti-bonding molecular orbitals
Why do higher orbitals have more energy?
Why is the antibonding pi bond higher in energy than the normal pi bond?


texts: Phenol vs 4-hydroxypyridine - Enol Content

texts:
Which has a higher enol content; phenol or 4-hydroxypyridine?

The solution to this question in my book says that phenol has a higher enol content due to aromaticity. But 4-hydroxypyridine is also stabilized by resonance. So how does that affect enol content?


texts: Biodegrability of straight chain and branched chain detergents

texts:
From NCERT Chemistry: Textbook for class XII, Part II [1, p. 461]:

Main problem that appears in the use of detergents is that if their hydrocarbon chain is highly branched, then bacteria cannot degrade this easily. Slow degradation of detergents leads to their accumulation. Effluents containing such detergents reach the rivers, ponds, etc. These persist in water even after sewage treatment and cause foaming in rivers, ponds and streams and their water gets polluted.
These days the branching of the hydrocarbon chain is controlled and kept to the minimum. Unbranched chains can be biodegraded more easily and hence pollution is prevented.

Why are straight chain detergents generally biodegradable while branched chain detergents are non biodegradable? Basically, how does branching affect biodegradation?
Is there any more detail/ better explanation than this or explanation from any other view point?
References

NCERT. Chemistry: Textbook for Class XII. Part II, Reprint: August 2019 Bhadrapada 1941; M. Siraj Anwar, Shveta Uppal, Arun Chitkara, Bibash Kumar Das, R.N. Bhardwaj, Mukesh Gaur, Series Eds.; National Council of Educational Research and Training: New Delhi, 2007. ISBN 978-81-7450-716-7. (PDF)


texts: Benzyl (3,4-difluorophenyl)carbamate reaction with epoxide in basic conditions

texts: I attempted this mechanism, however I am uncertain if I am correct.


texts: How come ∆G ≤ 0 is used for spontaneity in electrochemistry, not ∆G ≤ W(other)?

texts:
The spontaneity condition for a system at constant temperature and pressure in which the only type of work accomplished is of the $pV$ type can be expressed as:

$$\Delta G\le0\tag1$$

In case of other types of work (such as electrical, friction, etc.) there is an additional term and the previous equation becomes:

$$\Delta G\le W_\text{other}\tag2$$

In case of an electrochemical process the maximum work is the electrical work and can be expressed as:

$$W_\text{other}=-nFE\tag3$$

Question: Why it is still said that the electrochemical reaction is spontaneous if the change in Gibbs free energy is lower than zero, thus using Equation $(1)$, even though the proper equation to be used is number $(2)$?


texts: What mass of fragrances does a cubic meter of air contain on average?

texts:
What mass of fragrance are airborne in scented environments for example in a perfume deparment?

What is the minimum g/m3 of fragrance that a human can detect, and how much is present when it evaporates from an oven, in a cookie shop, from a cut lawn, near a perfumed lady and average levels from a day of walking.

What range of fragrance concentrations do humans typically have to cope with.


texts: What causes methane to have 25 times higher global warming potential than CO2

texts:
What causes methane to have 25 times higher global warming potential than $\ce{CO2}$?

I think it has to do with $\ce{CH4}$ being a less massive molecule, but I'm not sure.


texts: How much does a light heat the air around it?

texts: My dad told me to turn off the lights when I'm not using them because it will keep the house cooler. I don't think he is correct that a light can heat up the room. How much of a difference in the temperature would it make? Assume a 60 Watt light bulb running for one hour in a room with approx. 3000ft^3/85m^3 of air. Also assume the air is dry and in constant thermal equilibrium at 1 atm. I think the specific heat capacity of air is about 1 J/g*K, but I am not confident.


texts:
It has been a little over a year since the last synthesis-golf was posted. I have talked to orthocresol and would like to help revive the tag!
A full FAQ post has been written on chemistry.meta.SE, explaining the premise of synthesis golf and the 'rules'. Please take a look at this before answering (if you haven't already).

Hyperielliptone HA is a phloroglucinol extracted by Wu et al1 in 2008. The compound is of particular interest because of its highly unique structure and demonstration of  DNA oxidation inhibition.

Rules:

Your synthesis must involve a method for the preparation of the phloroglucinol core.
Your synthesis must be stereoselective; however, the stereocenter attached to the phloroglucinol core can be racemic. Bonus points if you can develop a stereoselective synthesis for this moiety!
All reagents must be available from Sigma Aldrich.
If you do not have time to complete the entire synthesis but have a clever idea for a specific moiety, feel free to share your answer.

References

Wu, C.; Yen, M.; Yang, S.; Lin, C. Phloroglucinols with Antioxidant Activity and Xanthonolignoids from the Heartwood of Hypericum geminiflorum. J. Nat. Prod. (2008) 71 (6), 1027-1031. DOI:10.1021/np8001145.


texts:
Coffee served hot can be quite bitter (presumably high pH).

Several people I have known will add a single grain of salt to the coffee - which reduces the perceived bitterness.

My question is: What is the reason a grain of salt alters the perceived bitterness of coffee by such a high degree? Can you explain the pH change that is occurring during this reaction?


texts: How to easily distinguish salts physically? Edit

texts:
I have basically 12 salts to identify in exams. They are ***

  Ammonium Carbonate, Ammonium Sulphate, Ammonium chloride, Aluminium
  Nitrate , Aluminium Sulphate, Barium chloride, Calcium Carbonate,
  Magnesium Carbonate, Magnesium Sulphate, Lead Nitrate, Zinc Sulphide,
  Zinc Sulphate

***. I will be given one of them. I know all the tests I have to undertake to identify these salts (such as ash test, flame test, sodium carbonate extract tests etc). But I would like to know if there is any quick way to easily identify my salt on looking it or some easy tests so that I get a leverage over time and could finish my tests easier. I would like to know ASAP, as I have my exams tomorrow.

Thanks in advance


texts:
What is the boiling point of an aqueous solution that has a vapor pressure of $23.0~\text{Torr}$ at $25~^\circ\text{C}$?
$(P^\circ_{\ce{H2O}}=23.78~\text{Torr};~K_\mathrm b= 0.512~^\circ\mathrm{C\ kg/mol})$

To solve this I used the equation $\Delta T_\mathrm b =m\times K_\mathrm b$. I calculated a molality of $1.88247\ \mathrm{mol/kg}$ which I then used to calculate a boiling point of $-0.9638\ \mathrm{^\circ C}$. This answer is apparently wrong and I don't understand why.


texts: Reference conditions for balances on nonreactive processes

texts:
In one of the examples in my book (Elementary Priniciples of Chemical Processes) where I am asked to calculate the rate of heat input required to heat a stream of methane and air from 20°C to 300°C, two references conditions are chosen (see picture).

In the text below the box it says "The reference condition for methane was chosen so that $H_{in}$ could be set equal to zero, and that for air was chosen so that $H_{in}$ and $H_{out}$ could be determined from Table B.8."

Why isn't it that $H_{in}$ for air is set equal to zero since the specific enthaply for air at 25°C and 1 atm is 0? How did they get that $H_{in}$ for methane should be zero?


texts: Why does Potassium Sorbate have two CAS numbers? - Should these not be unique?

texts: Potassium Sorbate has two CAS numbers - 24634-61-5; 590-00-1. Should these not be unique?


texts: Why are the densities of europium and ytterbium anomalously low?

texts: Why do europium and ytterbium have lower densities than expected in comparison to other lanthanides? I know it has something to do with the fact that they have half-full and full 4f subshells in the +2 oxidation state, but how exactly does it relate to density? And how does it affect the melting point?


texts: Does CH3COOH + H2O (vinegar) lose its antibacterial and antiviral properties when exposed to air?

texts:
I have been reading about using CH3COOH + H2O (vinegar) as a mild antibacterial and antiviral agent.  For example: https://pubmed.ncbi.nlm.nih.gov/15698693/
Note, before anyone gets confused (or concerned), this has nothing to do with the SARS-CoV2 virus which causes COVID-19.  I strongly doubt vinegar is effective at killing a coronavirus, and everything I have read confirms that doubt (the pH is too high, for starters).
Now, back to the topic at hand.  Does CH3COOH + H2O lose its antibacterial and antiviral properties when exposed to room temperature air for a long duration (over 8 hours, but less than 500 hours)?
I've been trying to find scientific articles regarding this, and so far, have not found anything helpful.
Ideally, I would love to see one or more graphs that plot effectiveness along one axis and time duration of air exposure along the other.  Of course, tables with data points would be equally welcome.
Note that I'm not looking for anything exact, as there are too many variables to be precise without getting into minute details.  I'm looking for a general idea of the changes (if any) over time as CH3COOH + H2O is exposed to room temperature air.


texts: How to separate lead condensate from aluminum

texts:
A common problem in shooting sports is precipitation of lead onto aluminum suppressor baffles.  (The lead presumably comes from both lead styphnate priming compound and from the base and bearing surface of lead bullets that vaporize during propulsion.)

If the lead precipitate is allowed to build up a contiguous layer it requires mechanical removal, which tends to damage and degrade the aluminum alloys used.

A common solution for ferrous baffles is to strip the lead with H2O2-boosted acetic acid, but that goes after aluminum almost as fast as lead.

What practical electrochemical methods could be used to strip the solid lead from the aluminum?

(Bonus if you can propose a method that would also leave titanium baffles intact!)


texts: How can I analytically calculate the rate of thermal decomposition of calcium carbonate?

texts:
I am a first-time poster on Chemistry StackExchange, and not much of a chemist.
I'm trying to determine the rate of thermal decomposition (in mol/s) of calcium carbonate ($\ce{CaCO3}$) at various temperatures (assuming atmospheric pressure).
The best resource I could find was an old handbook about the thermal decomposition of carbonates, which gave the equilibrium constant K for this reaction at various temperatures:

From this data set, it appears that the reaction only proceeds at temperatures above 1100 K. Below this temperature, all values of K are less than 1. A value of K = 1.84 is given at 1200 K, but no further information is provided.
I essentially have three questions:

Is it possible to use K to calculate a reaction rate? Specifically, for this example, would it be possible to calculate what the rate of reaction is, in mol/s, at 1200 K, using the given K value of 1.84?

If #1 is possible, is it also possible to extrapolate the rate of reaction to higher temperatures using the low-temperature equilibrium constants? I'm mainly interested in temperatures in the range from 1200 - 1800 K.

If neither of the above are possible, do I simply need to find (or produce) experimental data on the rate of reaction?

Thank you!


texts:
Recently started on NMR spectrum, and I'm slightly confused about chemical shifts and their connection to the resonance frequency and magnetic field.
From what I know, the "new" way of doing NMR means keeping the radio-frequency constant and increasing the external magnetic field in small increments.
Now, I believe a greater electron density around the protons (more shielded) will protect the positive nucleus from the external magnetic field and thus, the positive nucleus experiences a lesser net magnetic field. Hence, there is a lower resonance frequency which should result in a smaller chemical shift (the magnetic field will determine the energy differences between the spins).
From what I understand, because of experiencing a lesser net magnetic field, we increase the external magnetic field so that we can get a reading (this apparently gives rise to the idea of high field on the more shielded side). However by increasing the external magnetic field, won't we increase the energy differences between the spins and cause the resonance frequency to be higher which conflicts with the idea that we have a lower resonance frequency?


texts: Can water electrolysis detect the water impurities?

texts:
A salesman came to my house to demonstrate his water purifier machine which is a RO Purifier. To show the difference between his purifier machine and the machine I own, he took some water from my machine in a glass. Then he pour water from a bottle he bought in another glass claiming that this was a purified water from his machine (little suspicious). Then he put a small electrolysis machine (that one we used for experiments in school) on both glass and started it. After a minute, there was lot of uhh... particles looking like mud floating in my water, while in his glass, there were very few in dissolved state.

So he said that those particles were salts and bad impurities which my purifier can not filter out, and his purifier can, thus having few particles in his glass.
So my question is, can this method detect the impurities in water, or is it just some dirty sales tactic? Because as I remember, i was taught in school that electrolysis does not has to do anything with water, it just transfer cathode to anode or something like that (sorry for my bad chemistry knowledge :P)

Please help me out!


texts: How are phosphoglycerides different from phospholipids?

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(Currently studying high-school Biochemistry)

I'm unable to distinguish between phospholipids and phosphoglycerides from their "definitions" (Courtesy: Wikipedia)

On phospholipids:

Which suggests that phospholipids necessarily contain a glycerol "bridge" that connects the fatty acid tail to the phosphate head. To me, this looks like,

On phosphoglycerides:

"Glycerol-based phospholipids"?! But aren't phospholipids already 'glycerol-based'?

If both phospholipids are glycerol-based, and if phosphoproteins are "glycerol-based phospholipids"...how are they any different?

What am I missing here?


texts: I can't choose the set of 3 chemicals with each of which Si will react (out of 5 possible sets)

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This is one of the questions used in the Russian State Chemistry Exam. One needs to select the set of chemicals in the second column such that each of them would react with the element or chemical in the the first column.

I mean, it should react with each element in the set in order for that set to be suitable.

It seems to me that $\ce{Si}$ has no suitable set among those five.

It does not react with $\ce{Na2CO3}$ (that excludes set 1), with $\ce{HCl}$ (set 2), with$\ce{MgO}$ (set 3), with $\ce{H2SO4}$ (set 4) and with$\ce{Al(OH)3}$ (set 5).

I used Chemguide and a Russian school curriculum-based website to refresh my memory of $\ce{Si}$ activity.

Am I wrong in regard of any of the five chemicals? Maybe it will react with $\ce{MgO}$, for instance?


texts: Why is the graph of fluorescence vs. wavelength continuous?

texts: If the emission of a photon from an excited state to the ground state occurs with a precise energy, then why is it that wavelengths that differ from lambda max have values on a fluorescence vs. wavelength graph?


texts: How can we tell whether a phenomena was a chemical reaction or not?

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I mean in principle, in general.

How can we tell if some phenomena was a chemical reaction(s)? Change in physical properties cannot be since large-scale structural change can change physical properties as well, like heat treatment of steel. And what about changing diamond into graphite by heating. Hence, assuming there are only chemical and physical properties, only a change in chemical properties implies chemical reaction. But how do we know if chemical properties changed? Observing chemical reactions of the result(s). But how do we know what happens is a chemical reaction? A different instance of the same problem, which we started with.

How can anyone sure claim that a chemical reaction happened, or equivalently that some sample is a different substance and not just an allotrope or has larger "grains" for example?

Maybe mass or energy change can rule out those cases?


texts: Why do chemistry and physics have different sign convention in thermodynamics?

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In physics class, we write the first law of thermodynamics as $\mathrm dU =\mathrm dQ - \mathrm dW$ and in the physical chemistry class, we write the same law as $\mathrm dU =\mathrm dQ + \mathrm dW$.

The reason being the sign convention is different in both the cases.

In physics we take work done by the system as positive and in chemistry work done on the system.

I realize that this does not cause any change in the actual law of nature but I just want to know why we have different sign conventions. Wouldn't just one convention make life easier?

Is there a historical reason? Or is this is to differentiate between subjects?