texts: Are petroleum-based products prone to produce hard residues with black powder?

texts:
A common controversy about black powder is lubricant composition. Some people tell this is a bad idea to use any petroleum based products in such lube because it will produce hard, difficult to clean residues.

As far as I know, in the old days, gunners used mostly mutton tallow in order to lube their bullets, and most animal-based grease have been found an easy (available) and efficiant way for that use.

Now we can avoid the problems of stinking, liquifying or decaying animal greases, and some people tell they used petroleum jelly or lithium grease for decades with no particular problems. Unfortunetaly, other people disagree, and the exact recipes are so numerous nobody can give me rationnal and definitive answer.
Looking at classic lube recipes teach us there is no consensus on such questions :

  Historical Black Powder Bullet Lubricants

  Composition of Extensively Used Bullet Lubricants

  (E.H. Harrison, American Rifleman, Jul. 1965)

  U.S. Army 1855 - 1 beeswax, 3 tallow.
  U.S. Army 1861 - 8 beeswax, 1 tallow.
  U.S. Army 1873 - 8 bayberry wax, 1 graphite.
  U.S. Army 1880 and thereafter - Japan wax.
  Sharps Rifle Co., 1878 - 1 beeswax, 2 sperm oil.
  Massachusetts Arms Co. (Maynard rifle), 1890 - 1 beeswax, 3 tallow.
  Marlin Firearms Co., 1891 - 1 beeswax, 4 tallow.
  Smith & Wesson, 1891 - tallow.
  H.M. Pope, about 1900 - 3 mutton tallow, 2 bay wax, 1 beeswax, 1 steam cylinder oil, .2 of 1 acheson graphite. The bay wax could be
  omitted.
  Automobile door latch stick lubricant, U.S. Patent 1,920,161
  (1931) - 5 paraffin wax, 3 petroleum jelly, 2 oil.
  A large police department, 1962 - 1 beeswax, 1 paraffin wax, 1 cosmoline. Notes: "Cosmolene" in this context refers to dark
  petrolatum with no anti-corrosion additives. Refined yellow petrolatum
  (petroleum jelly, Vaseline) may be substituted.
  Any mixture containing paraffin wax must include a plasticizer, such as petrolatum. Microcrystalline petroleum waxes may be used
  as-is.
  The 1:3 beeswax/tallow mixture (or any composition composed mainly of tallow) is probably the most traditional choice for "primitive"
  shooters. The 8:1 mixture is rather stiff, and better suited to
  conicals, paper cartridges, and the like. For paper-patched bullets,
  I'd be inclined to try the Sharps formula, substituting Dexron II/III
  automatic transmission fluid for the sperm oil.

Could someone explain or quote some good source explaining if and why petroleum based lubricant will produce such disagreement with black powder?


texts: Help me proving Dalton's law of partial pressure formula

texts:
How do I prove

  $${{\displaystyle p_{i}=p_{\text{total}}y_{i}}}$$

where $y_i$ is the mole fraction of the $i^{th}$ component in the total mixture of $n$ components ?

Here is what I know

Mathematically, the pressure of a mixture of non-reactive gases can be defined as the summation:

${\displaystyle p_{\text{total}}=\sum _{i=1}^{n}p_{i}}$

or

${\displaystyle p_{\text{total}}=p_{1}+p_{2}+p_{3}+...p_{n}}$

And mole fraction $y_i= \dfrac{n_i}{n_{\text {total}}}$

I don't see how to relate , please help.


texts:
I have used Davies equation to find what I believed was single ion activities and multiplied them on concentrations to define the thermodynamic dissociation constants for any kind of buffer to find equilibrium conditions. Thereby I could reproduce major findings in recent publications which apparently used the activity coefficients obtained from Davies equation in a similar way.
Now I hear from a reviewer:

Unfortunately a misunderstanding about calculated "single-ion activity coefficients" is being promoted in the manuscript.
From a mathematical expression for the mean activity coefficients an expression for single ion activity coefficients can be derived. But these single ion activity coefficients have no physical or thermodynamic meaning.

I know a heated debate on this issue has been going on. Wonder if any proposals for armistice could be suggested.
Perhaps to clarify my predicament, what I understand as single-ion activity are such as the "fs" in $$K_{12}=f_1[H^+]f_2[HA^{2-}]/f_1[H_2A^-]$$ to define the thermodynamic dissociation constant of a buffer.


texts: Is it true that todays crude oil is getting more 'dirty'?

texts: I heard that crude oil, which is used to make other products like gasoline, is getting contaminated more and more by atoms like nitrogen and metals, so that the catalysts have more difficulty making it clear for gasoline. If so what causes these contaminations?


texts: Reason for inconsistency in specific gravity of calcium choride added to water

texts: I am seeing a significant change in specific gravity of products upon addition of $\ce{CaCl2}$ to water. The mass and volume of what goes in doesn't match my total specific gravity of what comes out. I am curious as to why that is the case?


texts: Isobaric-isothermal ensemble with degeneracy

texts:
I've been studying statistical mechanics for a while, the topic is very far from what I've learned till now so my questions may be superficial. When trying to see what my entropy is in an isobaric-isothermal ensemble, which turns out to be applicable in reactive systems, if I write my partition function $\Delta$ without the degeneracy factor $\Omega$, the answer I get from

$$S = \sum p_i\ln p_i$$

is

$$G = -T\ln\Delta$$

(with $T$ in energy units, $k_\mathrm{B} = 1$). However, if I take my systems to be in favor of a state or degenerate, I get

$$G + T\ln\Omega = -T\ln\Delta$$

Anywhere I read about this ensemble, the relationship for $G$ is in the first form and not the second, can someone give hints to some reading for what I'm missing here?


texts:
$\ce{Mn}$ in  $\ce{KMnO4}$ is in $+7$ oxidation state, has no d electrons so  d-d transition is not possible.

Then, how is $\ce{KMnO4}$ coloured?


texts: Calculating the molar mass of a gas given state function values

texts:
Question:

  A gas has a volume $255\ \mathrm{mL}$, a pressure $733\ \mathrm{mmHg}$, a temperature $548\ \mathrm{^\circ C}$, and a mass $1.22~\mathrm{g}$. What is the molar mass?

My attempt:

$$pV = nRT$$

Convert $733\ \mathrm{mmHg}$ to $\mathrm{atm} = 733~\mathrm{mmHg} \cdot 1\ \mathrm{atm}/760~\mathrm{mmHg} =   0.9645\ \mathrm{atm}$

Convert $\mathrm{^\circ C}$ to $\mathrm{K}$: $548\ \mathrm{^\circ C} + 273.15\ \mathrm{K} = 821.15~\mathrm{K}$

Convert $\mathrm{mL}$ to $\mathrm{L}$: $255~\mathrm{mL} \times \frac{1~\mathrm{L}}{1000~\mathrm{mL}} = 0.255~\mathrm{L}$

$$0.9645\ \mathrm{atm} \times 0.255~\mathrm{L}= n \times \frac{0.8206~\mathrm{L\cdot atm}}{\mathrm{mol\cdot K}}  821.15~\mathrm{K}$$

$$\frac{0.2459}{673.84} = n \times \frac{673.84}{673.84}$$

$$0.000364\ \mathrm{mol} = n$$

$$M = \frac{m}{n} = \frac{1.22~\mathrm{g}}{0.000364~\mathrm{mol}} =   3351.648$$


texts: Why is C=C launching electrophilic attack on Bromine instead of the other way round?

texts: So during my lecture on reaction of Alkenes with Halogens, my lecturer used the example of $\ce{Br2}$ gas reacting with $\ce{CH2CH2}$. He mentioned that the $\ce{C=C}$ launches an electrophilic attack on the electropositive Bromine atom (the one that is nearer to $\ce{CH2CH2}$) and I'm wondering why is the $\ce{C=C}$ launching the electrophilic attack? Shouldn't it be done by the Bromine gas since the $\delta^+ \ce{Br}$ is electrophilic and needs the electrons so it attacks the double bond which is most electron dense?


texts:
Ok, so let's say I have raw silver which is polluted with a bit of gold, copper and lead.
So through electrorefining I want to make pure silver out of it.

Let's say I have it all in an acidic solution. What happens when I turn on the Voltage?
How would I prevent the other elements from getting electrolyzed?
Because when I have the electrorefining of copper it gets clean even when polluted with silver, so why doesn't the copper get electrolyzed as well?


texts: Help understanding the pi-properties of the NCS- ligand

texts:
Course knowledge

When considering the NCS- ion, I take all atoms to be sp hybridized. This means that there are 8 electrons that are accommodated in the $\pi$-system.

There are two orthogonal 3-orbital 4-electron pi systems: similar to the allyl anion, each made of an antibonding, non-bonding and bonding set. The bonding and non-bonding orbitals are occupied in this system. As the non-bonding orbitals are both full of electrons, NCS- therefore can act as a $\pi$ donor.

The above is what I have been taught, however I am confused with this rationalisation when comparing the positions of NCS- and SCN- in the spectrochemical series.

Spectrochemical series

SCN- is a weak field ligand, which comfortably suggests that it is a $\pi$-donor. However, NCS- is relatively high field, and is therefore a $\pi$-acceptor - which disagrees with what I've been taught. As sulfur is less electronegative than sulfur, it is higher in energy and therefore contributes more to the anti-bonding orbital.

Questions

Wouldn't this mean that SCN- would be the better $\pi$-acceptor rather than NCS-? Or is it the case that since sulfur is larger than nitrogen, the better orbital overlap with the transition metal favours donation?

Additionally, how can we say that the pi-donation from the non-bonding orbitals wins out over the pi-acceptance from the anti-bonding orbitals? Is it because the anti-bonding orbitals are involved in the ligand bonding whereas the non-bonding orbitals are not?

Also, why is NCS- a pi-donor (according to what I have been taught) even though it is relatively high field?


texts: Melting temperature and electronegativity trends in transition metals

texts: So I know that generally the melting temperature increases across the row (let's look at just the first row for now) but what are the deviations? And why do they occur? I've looked everywhere online and can't find a clear answer to this.


texts: I am working on fabricating the icyball system. I am planning to charge it with the help of convex mirrors. Whether it is necessary to create a vaccum inside the refrigeration closed cylinders before filling ammonia?


texts: Can the regions of 1s and 2s subshells overlap?

texts:
I was studying atomic orbitals and always had this question lingering.

As we can see in the image, the 1s and 2s subshells both are known to closely surround nucleus. The overlapping peaks in the graph (of probability vs radius) lead me to believe that the part region of 2s before the node should overlap with the region under 1s.

And by 1s and 2s I mean their contours ( regions which contain 90% probability of electron occurring).

Am I committed a blunder here or do subshells overlap?

Additionally, does the same logic apply when comparing the spatial distribution of say 2p and 2s aswell? Do they have overlapping regions of high electron probability density as well?


texts: Can the van der Waals coefficients be negative in the van der Waals equation for real gases?

texts:
A gas described by van der Waals equation has the pressure that is lower than the pressure exerted by the same gas behaving ideally. True or false?

My approach

$$P(\text{ideal}) = P(\text{real}) + P(\text{changes due to intermolecular forces})$$

So the pressure of real gas can be more as well as less than that if a gas behaving ideally depending on whether intermolecular forces are repulsive or attractive in nature.

Questions

The answer to the question is given as True. So I want to understand what is wrong about my approach.
Since the intermolecular forces depend on $a$, for attractive nature $a$ is positive. Is $a$ negative for repulsive nature of forces?


texts: Reaction mechanism of lithiated benzene and oxygen in acid

texts:
According to (1) addition of O2 in acid to lithiated benzene makes phenol.

I'm trying to deduce the mechanism, and somehow it doesn't feel right but I'm not sure.

(1) Snieckus, V. Directed ortho metalation. Tertiary amide and O-carbamate directors in synthetic strategies for polysubstituted aromatics. Chem. Rev. 1990, 90 (6), 879–933. DOI: 10.1021/cr00104a001.


texts: Does cathodic protection work for air oxidation?

texts: I'm not expert in cathodic protection, but does it work with metals under air oxidation? Is it possible to protect a metal from air oxidation by applying an electrode to it? Or it has to be inside an electrolytic solution like sea water?


texts: What workflow can I use on to extract cartesian coordinates of many molecules from both .spartan and .out (Gaussian) files?

texts:
I'm searching for a workflow for extracting cartesian coordinates for multiple moelcules from both a single file (e.g., several conformers from one .spartan file or one multiple molecules, each from multiple Gaussian output files). Any insight would be appreciated. I'm using Ubuntu (14- & 16.04), on a machine on which I do not have either Gaussian or Spartan installed.

Thank you kindly


texts: Under what conditions can epoxide undergo oxidation by HIO4

texts:
Question

Doubt

Can epoxide react with HIO4. I have  seen that in same cases they do. But in this given question they don't.  If they do react , then how  and what will be the products?Please help


texts:
Is time a measurement of entropy? Is it because time is increasing forever?

Well after reading about the Second Law of Thermodynamics and working with Entropy, I began to realize that if time can be interpreted as a measure of Entropy, since it is always increasing.

  Since almost everything decays with time, I thought that time could be
  a measure of Entropy. Since it is achieving the lowest energy state
  possible.

Thanks


texts: Why are both products observed due to Molecular Orbital theory

texts: I can reason out the first product as the highest occupied orbital of one excited molecule is approached by the lowest unoccupied orbital of the ground state molecule. I cannot rationalize the second product; am I missing an aspect of MO bonding that is important?


texts: Apparent contradiction in the name of group 2 elements

texts:
From my understanding (I might be very wrong), the "earth" in alkaline earth metals means non-metallic, insolube in water and resistant to heating, therefore the oxides and hydroxides of group 2 metals should be insoluble in water by definition of "earth".

However, doesn't the term "alkaline" by definition mean bases that are soluble in water? How can the two definitions be co-applicable?


texts: 50-90'C color changing chemical to use as warning marker for hot electronics?

texts:
I am testing electronics with many potentially unstable contacts, and I wish to monitor if they rise above 50 to 90 degrees Celsius, i.e. using carbon paper that would darken progressively from 50 to 90.

The substance should stay a specific warning color if it goes too high and not change hues again same as thermochromic pigment, so that I can detect high temps.

I hope you know a chemistry trick that could help? Thank you.


texts: How does pH affect the spontaneity of biochemical processes?

texts:
A decrease in $\mathrm{pH}$ increases the hydrogen ion concentration, thereby decreasing $Q,$ and decreasing Gibbs free energy as mathematically expressed:
$$\mathrm dG =\mathrm dG^\circ + RT\ln Q$$
This means that the more acidic the environment is, the more spontaneous the reaction is. But don't biochemical processes operate at approximately neutral $\mathrm{pH} = 7,$ so enzymes function optimally (does not denature)? But why does the equation favor spontaneity at (for example) $\mathrm{pH} = 3$ than $\mathrm{pH} = 7?$
For specific case, such as the biological oxidation of ethanol? Does it mean that it will thrive at acidic environment based on the equation? But how can we explain for the specificity of biological reaction operating at their optimal pH ranges?
For example, in the stomach it requires an acidic environment so the equation holds true. But what about for other biochemical processes that operate at neutral pH (the equation cannot explain it)? Or is there actually another equation to utilize to explain how spontaneous biochemical reactions can be?


texts:
In a question it is given that consider $H-X$ chemical bond and find $H-X$ bond distance for which there is zero probability density of finding the proton. It is easy to solve we have just to calculate the position of nodes of wave function of corresponding harmonic oscillator.

But my question is does the wave function of harmonic oscillator gives the probability density of both electrons and protons of bonded atoms which behaves as harmonic oscillator? As while I was reading the chapter, initially I thought that $\psi$ only gives the probability amplitude of electrons if we extend harmonic oscillator concept to bonded atoms.


texts: Why is ethanol used in catalytic reduction of nitro group to an amine?

texts:
$$\ce{R-NO2 +C2H5OH + H2 (g)->[Pt/Pd/Ni] R-NH_2}$$

The above equation represents catalytic reduction of nitro group to amine. What is the role of ethanol in it?

I understand that $\ce{Pt/Pd/Ni}$ plays an important role as reducing agent and hydrogen gas replaces oxygen atoms. But, I'm not able to understand the role of ethanol. Can someone help me with this?


texts: Is the flame temperature of a burning fuel affected by pre-heating the fuel?

texts:
This page on Adiabatic temperatures helpfully lists the theoretical maximum temperatures that flames will reach under certain conditions for a number of fuels. They assume initial atmospheric conditions of 1 bar and 20 °C.

However, I am remain confused about what would happen if the fuels (and air) were pre-heated to temperatures close to these maximums before they were mixed and ignited.

Would the flame temperature then be higher than these listed maxima?

Would the reaction be slowed down by the higher temperature? (I understand that this might happen for exothermic reaction in equilibrium with an endothermic one, but I don't think that describes burning fuel.)

Is there some other mechanism that prevents the flame temperature from exceeding these minima?

This question was inspired by discussion on a Skeptics.SE question similar to this closed Chemistry.SE question about jet fuel and steel beams. I think it is sufficiently focussed and apolitical to be on-topic here. My background level is an ancient undergraduate science degree; I have forgotten more chemistry than I remember.


texts: What would be the name of this compound?

texts: Although I assume this compound is likely unable to be formed, my chemistry teacher put it up on the whiteboard to show the extent of what you can name using IUPAC nomenclature, out of interest I tried to name it and got hexcyclo[2.2.0.0.0]cyclohexane, is this correct or am I mistaken?


texts:
There is an explanation of how a battery works that says that inside the battery, the electrons do a complete loop and can return to their starting point. When the electrons arrive in the positive terminal and they lost all of their potential energy, the battery does work on the electrons to  put them back in the negative terminal so they are full of energy and reenter the circuit.

This explanation is very great because it answers questions : why does putting 2 batteries in series double the voltage? (because work has to be done two times on the electrons in the battery, so the potential energy doubles). Why connecting - of battery 1 to + of battery 2 without connecting + of battery 1 to - of battery 2 doesn't create electricity (because the electrons have to do a complete loop in the circuit and return to their starting point to make electricity for a long time. There is no external wire connecting - of battery 2 to + of battery 1 so there isn't a complete loop).

However, from what I understand of batteries, there is no electron that moves from the positive terminal to the negative terminal of the battery. The electrons of the circuit all come from the negative terminal and once they reach positive terminal there is nothing else happening except making the electrolyte ions neutral. They don't return to their starting point.

So could someone prove to me that inside a battery, electrons from the positive terminal are done work on and go to the negative terminal.

Or if this theory is false, could someone answer the two questions above that are easily answered by this theory in another way?


texts:
The Question:

How many liters of $H_2S$ would be required to react with excess oxygen to produce $12.0$ $L$ of $SO_2$? The reaction yield is $88.5$%. Assume constant temperature and pressure throughout the reaction.

My Approach:

I used dimensional analysis to convert from liters of $SO_2$ to $moles$ of $H_2S$ and then used Avogadro`s Law ($\frac{V_1}{n_1} = \frac{V_2}{n_2}$) to find the volume of $H_2S$ in liters.

Dimensional Analysis:
$\frac{1}{.885} * \frac{12.0L}{1} * \frac{1 g}{1 mL} * \frac{1 mol SO_2}{64g} * \frac{2 mol SO_2}{2 mol H_2S} * \frac{1 mol H_2S}{34 g} = 6.23$ $mol$ $of$ $H_2S$.

Avogadro`s Law:
$\frac{12.0L}{166 mol} * \frac{ L }{6.23 mol}$

End Result = $.028 L$

^ The end result does not seem right and any help in remedying my approach or shedding light on another approach would be much appreciated. Thanks in advance!


texts: Find the Total Pressure When the Faucet is Released

texts:
Two chambers are connected as shown in the figure. The total pressure of the first chamber that contains Ar and He gas is 98.4 atm. If the faucet is released, find the total pressure. (There's 1 mol of Nitrogen gas on the second chamber)

(A) 52.2 atm (B) 61.5 atm (C)98.4 atm (D)123 atm (E)172.2 atm

My attempt:

Because of Ar and He are inert gas I only calculate the second chamber's partial pressure.

$$\begin{aligned}
P_2&=\frac{1\cdot0.082\cdot300}{1}\\
&=24.6\mbox{ atm}\\\\
P_{tot}&=P_1+P_2\\&=123\mbox{ atm}\\\\
\end{aligned}$$
My other attempt:
$$\begin{aligned}
n_2&=\frac{1\cdot98.4}{0.082\cdot300}\\
&=4\mbox{ mol}\\\\
n_{tot}&=n_1+n_2\\&=5\mbox{ mol}\\\\
P_{total}&=\frac{5\cdot0.082\cdot300}{2}\\&=61.5\mbox{ atm}
\end{aligned}$$

My question is which one is the correct method and why.


texts: Do metallic bonds contain London dispersion forces?

texts:
On our chemistry exam, a question asks "Which force is present between Fe particles? a) Van der Waals b) Metallic"

At first it seemed obvious that it was metallic; however, upon closer reading, it seemed like a trick question. First of all, there's no such thing as a metallic force. In addition, I'm not sure if Van der Waals forces exist for metallic bonds. If they do exist, then the answer was definitely "Van der Waals".

So my question is, would Van der Waals/London dispersion forces exist between particles of iron?


texts: What is the product formed when 4-chlorobut-1-ene is treated with acetic acid?

texts:
My teacher did like this forming a really unstable cyclopropyl group but this is the correct answer instead. My question is why the product will be even formed?
In the mechanism that my teacher had drawn he formed a really unstable carbo anion there whereas he could have formed a primary carbanion and next may it have formed a four membered ring.

Why did not the neucleophile (acetic acid) did not approach to the carbon atom with which the chlorine is attached directly? Forming

I tried to justify the answer then it came to me that if the acetic acid does approach from right hand side may it be forming a stable carbocation by resonance

And this next form a very stable cyclo propyl carbocation. (Which is one of the most stable carbocations) So which explaination should I rely on?
Thank you.


texts: Why is there a comparative lack of variety in positive counterions in drugs?

texts:
Pharmaceutical salts are important in the process of drug development. Using different chemical species to neutralise the parent drug can produce a diverse series of compounds, and this process is traditionally used to improve drug solubility and drug dissolution rates.

For negatively charged drugs which are paired with cationic counterions, there seems to be a general lack of variety in the counterion choice, which is usually a metal ion such as sodium. Other counterions such as ammonium cations (e.g choline and respective cations of benzathine, diethanolamine, diethylamine, meglumine, piperazine, procaine) or silver have not been used over the past 25 years.

On the other hand, there seem to be many more anionic counterions, most notably chloride, but also mesylate (e.g imatinib mesylate), besylate (amlodipine besylate), hydrocortisone succinate, and so on.

How can such a trend be explained in drug development process or chemistry of substances thereof? Could it simply be because there are fewer negatively charged drugs, or are there other explanations?


texts: Total entropy change for a spontaneous reaction

texts:
For the oxidation of iron,
$$\ce{4 Fe(s) + 3 H2O(g) -> 2 Fe2O3(s) + 3 H2(g)}$$
the entropy change is $ \pu{–549.4 J K^{-1} mol^{-1}}$ at $\pu{298 K}.$ In spite of the negative entropy change of this reaction, why is the reaction spontaneous? $(\Delta_\mathrm{r}H^\circ$ for this reaction is $\pu{–1648 kJ mol^{–1}})$

In this question the solution given is that we consider the total entropy change for the reaction, i.e. the entropy change for a system plus the entropy change of surroundings, and that comes out to be positive.
But shouldn't the entropy change for surroundings (calculated by $q_\mathrm{rev}/T)$ be the negative of the entropy change for the system (heat absorbed by the surroundings is same as the heat emitted by system)? Thus, shouldn't the total entropy change be zero?


texts: How is the pka related to the ph of the solution for an amine?

texts:
So was reading a magazine for competitive exams and this question is bugging me a lot.

How is pka values of a base associated with the pH of the solution. The solution for it is that the Nitrogens would remain this way and only the H from OH would be dissociated. That's obvious because the medium is basic and the acidic H would be dissociated, but what about the nitrogen atoms? How is the pka of a base represented? Is that the equilibrium constant for it's conjugate base?


texts: Energy loss in the process for exothermic reactions

texts: Some chemical reactions while producing the product molecules releases heat to the surroundings and such reactions are called “exothermic reactions”. Is it true that such systems must be showing energy loss in the process meaning “ΔE ” must be negative?


texts:
Recently insects are featured as a protein rich source for human nutrition. That humans can really digest chitin through chitinase enzym has been only recently confirmed.

But, does the chitin shell of their body actually count to the protein family?

Wikipedia does not state a clear yes or no. It says it is derivative of glucose, and may be compared by function to keratin protein. I'd really like to exclude any ambuguity and undersrand why.


texts:
I want to cast a cube out of super-absorbent powder (Fake Snow) for an art piece, and make it become shapeless by gradually exposing it to water over 7 days. I have 2 questions:

What is the best type of glue that I can use to stick it together while keeping it exposable to water + keeping them together after expansion?
Would it expand with slowly dripping water over 7 days? (All the videos I watched recommend "pouring water as quickly as possible")


texts: Reaction mechanism in fluoride adsorption to aluminum oxide

texts:
Despite a fair amount of research (excluding non-open access journals, to which I have not got access), I cannot seem to find an explanation of the process that takes place when $\ce{F^-}$ adsorbs to activated alumina ($\ce{Al_2O_3}$).

I do know that the process involves both chemisorption (monolayer formation) and physisorption, but since the latter is explained solely by van der Waals forces, I am primarily looking for an explanation of the former.

EDIT: Does adsorption take place only at the aluminium ions? If not, does that mean that all aluminium compounds with oxidation state +3 will be equally good adsorbents?

EDIT: I have found an article (https://link.springer.com/article/10.1023/A:1012929900113) which proposes a mechanism that involves aluminium-fluoride complex formation. If this is the case - why is this even classed as an adsorption reaction at all, and not just a normal chemical reaction? And what role do the $\ce{OH^-}$ ions play? Do they keep the aluminum in the ionic lattice of the alumina?


texts: Rearrangement considerations in feasibility of SN1 in given reactants

texts:
I have been asked to compare the feasibility of Unimolecular Nucleophilic Substitution ($\mathrm{S_N1}$) in the following question.

I have received instruction that the reaction will be feasible only in the first compound (which results in a 3° stable carbocation) since 1-chloro-1-methylcyclopropane is angle strained and the resulting carbocation in this case will be unstable.

However, if we consider the possibility of hydride rearrangement in the second molecule, after formation of the carbocation, the following rearrangement should stabilise the carbocation formed, through the delocalisation of sigma electron pair as is seen in the case of cyclopropyl methyl carbocations.

Where exactly am I going wrong?


texts: Is crushing an avocado a chemical or physical change?

texts: Applying pressure can result in chemical changes, does this hold true for an avocado?


texts:
I was looking at a graph of the internuclear distance vs. the potential energy, and the strongest H2 bond had the lowest potential energy.

Is this always the case?


texts: Can an alcohol oxidation to ketone happen with hydrogen peroxide?

texts: As far as I know, usually $\ce{CrO3}$ and $\ce{KMnO4}$ are used for this scope, but can other oxidizers such as $\ce{H2O2}$ be used?


texts: Why do acids usually completely react with bases?

texts: When a neutralisation reaction happens, for example, $ \pu{100 mol l^-1}$ of $\ce{HCl}$ with $\pu{100 mol l^-1}$ $\ce{NH_3}$, why does all of the base and acid get converted to salt? Why isn't there an equilibrium established between salt and acid-base?


texts:
We define chemical equilibrium as the point in a reaction where the rates of the forward and reverse reactions become equal. We also write

$$K_c = \frac{k_f}{k_r}$$

If at equilibrium the rate of the forward reaction and the rate of the reverse reaction become equal then their rate constants should also be same. If rate constants $k_f$ and $k_r$  become the same, then $K_c$ should always be equal to 1. However, the value of $K_c$ is not always 1. Why is it so?


texts: Pressure exerted by a particle of ideal gas

texts:
There is a step I fail to grasp in the proof that for a monatomic ideal gas, $U=\frac{3}{2}PV$, where $U$ denotes the internal energy of the gas.
The proof involves considering a particle with mass $m$ travelling with velocity $v$ inside a cube of side $x$. The particle is assumed to travel perpendicularly towards one of the sides before bouncing back off it. The force exerted by the particle at any instant is opposite to the force exerted by the side of the cube on the particle. The latter can be worked out using Newton's second law, prior to which we need to calculate the acceleration of the particle during the collision. Assuming the collision to be perfectly elastic, the change in velocity before and after the collision with the wall is $\Delta v=2v$. To work out average acceleration, according to me, one would need the duration $\Delta t$ of the collision, since assuming it to be instantaneous would imply infinite acceleration. However, the various proofs I've read assign to $\Delta t$ the time that is needed for the particle to bounce off the wall and return after colliding with the opposite wall, in other words $\Delta t=\frac{2x}{v}$. I really can't see how that $\Delta t$ is relevant to the force exerted by the particle on the wall during the collision.

[Edit :] If there are no considerations about duration of the collision, then theoretically, no two particles would ever collide simultaneously with the wall and therefore the wall experiences very frequent collisions with single particles.


texts:
I was looking into an article (doi: 10.1063/1.5058063) which presented a histogram of radius of gyration for samples of different configurations of alanine dipeptide. This property is fairly simple to calculate using
$$
a_{\mathrm{Rg}}(x)=\sqrt{\frac{\sum_{p} m_{p}|| x_{p}-x_{\mathrm{COM}}||^{2}}{\sum_{p} m_{p}}}
$$
The sum considers all atoms $p = 1, \dots, P$ of the peptide, where $m_{p}$ and $x_{p}$ denote the mass and the coordinates of each atom, respectively. $x_{\mathrm{COM}}$ denotes the center of mass of the peptide.

In a different problem, I have a number of molecular graphs generated by a network trained using QM9 dataset and am looking for properties that are readily calculable for the newly generated molecular graphs using such packages as RDKit and OpenBable.

The properties in the QM9 dataset itself, like LUMO energy and energy of atomization, need DFT calculation, which is not something that I look forward to do. An example of a property of interest is QED, which can be easily calculated using RDKit package. But QED is more of interest in ZINC dataset.

I'd appreciate comments on any easy to compute property of interest to the community for QM9 dataset.


texts: How can the hybridisation schemes of transition metal complexes be determined?

texts:
Lets say I have to find hybridisation of $\ce{[Ni(CO)_4]}$ and $\ce{[Ni(CN)_4]^{2-}}$.

The metal atom/ion in these compounds are $\rm Ni$ and $\rm Ni^{2+}$ respectively.

So the outer shell configuration for $\rm Ni$ in $\ce{[Ni(CO)_4]}$ would be $$\rm 4s^2  \ \ 3d_{xy}^2\ 3d_{yz}^1\ 3d_{zx}^1\ 3d_{z^2}^2\ 3d_{x^2 - y^2}^2 \ \ 4p^0 \ \ 4d^0$$

The electrons from s oribital will jump to d orbital and so I expect $\rm CO$ to donate electron pairs in $\rm 4p$ and $\rm 4s$ orbitals and form $\rm sp^3$ hybridisation.

The outer shell configuration for $\rm Ni^{2+}$ in $\ce{[Ni(CN)_4]}^{2-}$ would be $$\rm 4s^2  \ \ 3d_{xy}^0\ 3d_{yz}^1\ 3d_{zx}^1\ 3d_{z^2}^2\ 3d_{x^2 - y^2}^2 \ \ 4p^0 \ \ 4d^0$$

Here also I expect the electrons to jump from s to d and hybridsation to be $\rm sp^3$, but the answer given here is $\rm dsp^2$. Why ?

I am heavily confused with this hybridsation stuff, is there a systematic and logical way of knowing hybridsation of coordination compounds ?

I tried to search this topic on internet and I came across  $H = \dfrac12(V + M - I)$ where $V$ is number of valence electron, $M$ is number of single bonds and $I$ is charge on the atom. Here if $H= 2$ then it is $\rm sp$ , $H = 3$ then $\rm sp^2$ and so on.

For $\ce{[Ni(CO)_4]}$, here $V = 10$, $M = 4$ and $I = 0$, so $H = 7$ hence $\rm sp^3d^3$.

Also for $\ce{[Ni(CN)_4]}^{2-}$, here $V = 8$, $M = 4$ and $I = -2$, so $H = 7$ hence $\rm sp^3d^3$.

As it can be seen, this formula is complete failure.

Why this formula does not work for coordination compounds whereas it works for compounds like $\rm PCl_5,PCl_3$ and $\rm SF_6$ ?

In this answer the author makes the claim that $\ce{[NiCl_4]^{2-}}$ has hybridsation $\rm sp^3$ and $\ce{[Ni(H2O)6]^2+}$ has hybridsation $\rm sp^3d^2$. How did he know that ? This is my question not why hybridsation is not a valid theory to study coordination compounds.


texts: Does silicon dioxide react with alkalis?

texts:
In my science class, I have been taught that silica (silicon dioxide/sand) has three properties, namely

It does not react with water.
It does not decompose with heat.
It does not react with acid.

However I think that if it does not react with acid, will it react with bases? I am just curious because if it does react, why does my textbook not say anything about that?


texts:
The following reactions do not occur:
$$\ce{HCl(aq)}\ +\ \ce{Pb(NO3)4(aq)} \to$$
$$\ce{HCl(aq)}\ +\ \ce{Cu(NO3)2(aq)} \to$$

Is this because in both cases both reactants are entirely dissolved as their components ion?
$\ce{NO3}$ is a conjugate base of a strong acid  so it is a very weak base so it doesn't participate in reactions, right?


texts: At what point does decreasing solvent temperature cause a decrease in gas solubility?

texts:
Example: At constant pressure, carbon dioxide becomes less soluble in water as temperature increases. We also know that carbon dioxide becomes more soluble in water as temperature decreases.

Does introduction of order and loss of kinetic energy of solvent molecules eventually lead to a decrease in a solvent's ability to accommodate gas molecules? It is hard for me to believe that ice cubes can hold gas more effectively than the same volume of a glass of water.


texts: Limit to volume change in a discretized mathematical model?

texts:
I have set up a mathematical model describing the diffusion of ozone out of a gas bubble. The bubble is surrounded by a thin gas film. So actually, the model describes the diffusion of ozone through this gas film.
The mathematical model is created by discretizing the volume from $V_0$ to $V_1$. Where $V_0$ represents the outer volume of the bubble, and $V_1$ represents the outer volume of the gas film (surrounding the bubble). The discretized scheme consists of $N$ equally spaced volume elements from $V_0$ to $V_1$ (finite difference method):
\begin{equation}
    \Delta V = \frac{V_1 - V_0}{N}
\end{equation}
The volume of the bubble changes as a function of the amount of ozone leaving the bubble, which in turn changes as a function of time.
The volume of the bubble and the amount of ozone inside the bubble is linked by the ideal gas law:
\begin{equation}
    V_0 = \frac{n_\text{total}(t) \cdot R \cdot T}{P}
\end{equation}
$n_\text{total}$: the total amount of gas inside the bubble, $T$: the temperature, $R$: the gas constant, and $P$: the pressure.

The bubble does not only contain ozone. It also contains inert gases, so that:
\begin{equation}
    n_\text{total} = n_\text{ozone}(t) + n_\text{inert}
\end{equation}
$n_\text{inert}$ will remain constant and only $n_\text{ozone}(t)$ will change over time.

There should be a limit for how much the volume can change before numerical errors will start to occur. Beyond this limit, the discretization scheme should break down and cause errors. How do I express this limit?

Is the limit given by:
\begin{equation}
    \text{Ratio} = \frac{V_{0,\text{ initial}}}{V_{1,\text{ initial}}}
\end{equation}

So that the volume change must not exceed the ratio of the two initial volumes of the bubble and the gas film?

Link to cross-posted question on CompSci.SE.


texts:
Does a phase transition occur also for an ideal fluid (from ideal gas to ideal uncompressible liquid)?
Or ideal fluids can be modelled only as ideal gas or uncompressible liquid at all, without the possibility for a phase change?

I hope the question is well posed, thanks


texts: Why is the uncertainty of a digital instrument always the smallest scale division?

texts: For a mass balance that can give readings to 2 decimal places, the uncertainty is assumed to be $\pm 0.01$. Can someone explain the rationale for this, as I would think it more logical for the uncertainty to be given as $\pm 0.005$.


texts: Linking an electrochemical cell to an electrolytic cell

texts:
Electrolysis occurs when a non-spontaneous redox reaction occurs when electrical energy is put into it. An electrochemical cell functions by using two redox reactions to facilitate movement of electrons. So for an alkaline battery, the zinc anode will oxidize and release electrons, which will flow through the circuit to reach the manganese ($\ce{MnO2}$) cathode, which will be reduced, allowing more electrons to flow through the circuit without buildup of electric charge. I assume here that both reactions are spontaneous, and the electron buildup in the anode prevents further zinc oxidation when the circuit is incomplete.
$$\ce{Zn(s) + 2OH- (aq) \rightarrow ZnO(s) + H2O(l) +2e-} [E^\theta= 1.28V]$$
$$\ce{2MnO2(s) + H2O(l) + 2e- \rightarrow Mn2O3(s) +2OH- (aq)}\ [E^\theta= 0.15V]$$
If the alkaline battery is linked to an electrolytic cell, won't it just be like two electrochemical cells working in conjunction to each other? The zinc anode will be linked to the cathode of the electrolytic cell, and then the ensuing redox reaction will (probably) be spontaneous. So the "electrical energy" put into the electrolytic cell will be instead chemical energy?
Also, seeing that the $\ce{MnO2}$ cathode has a relatively small $E^\theta$ value, won't it be hard to trigger oxidation of the electrolytic anode? When connected to the electrolytic cell, do the cathode and anode of the electrochemical cell now work totally independently? If that is the case, the voltage of the battery should not be considered, but instead the electrode potentials of the anode and cathode, but that is usually not the case. What am I misunderstanding about this?
edit: I'm asking about the mechanism when an electrochemical cell is linked to an electrolytic cell, not about the reactions taking place in the electrochemical cell itself, so the question suggested doesn't quite fit the bill.
edit 2: Added a picture to better show my doubts. If the galvanic cell is linked to an electrolytic one as shown here, the galvanic anode and the electrolytic cathode are linked and seemingly acts as a separate cell. The same thing can be said about the other two electrodes. If this is the case, doesn't the galvanic anode and cathode each act independently of one another, and therefore the electrode potential of the individual half cell must be considered? If they are actually linked, how?


texts: Why m-hydroxybenzoic acid has higher acidity then p-hydroxybenzoic acid?

texts:
Why  m-hydroxybenzoic acid has higher acidity than p-hydroxybenzoic acid?

I have a reasoning that since hydroxy group is an activating group, then it increases the electron density on its para position. So for  p-hydroxybenzoic acid, the carbonyl carbon has a greater ability to share molecular orbital's electron cloud to its attached hydroxy group. So the hydroxy group doesn't release $\ce{H+}$ easily. But that's not the case for m-hydroxybenzoic acid.

Is it right?


texts:
What I understand by a spontaneous reaction is that - A reaction whose G is negative and which occurs without the input of energy.

Gasoline reacts with oxygen only if a spark is provided. So how can it be a spontaneous reaction?

Do nonspontaneous reactions occur in nature? If so, are they always slow? If they are slow then what is the difference between a slow spontaneous reaction and a nonspontaneous reaction?

Are nonspontaneous reactions active energies more than that of spontaneous reactions?


texts: Energy balance in battery thermodynamics

texts:
I am trying to understand the derivation of a general energy balance in battery thermodynamics. The following relation is frequently found to determine the heat generation of a battery:

$\dot{Q} = \dot{Q}_\text{rev} + \dot{Q}_\text{irrev} = IT\,\frac{\mathrm dE_0}{\mathrm dT} + I(E-E_0)$

where $\dot{Q}$ is the heat generation, $I$ current, $T$ temperature and $E$ cell voltage. The index $0$ denotes the open circuit voltage. Furthermore, $\Delta S = zF\,\frac{\mathrm dE_0}{\mathrm dT}$, with $F$ as Faraday constant and $z$ as number of exchanged electrons.

The derivation is as follows:

First law of thermodynamics: $\mathrm dU = \mathrm dQ - \mathrm dW \tag{1}$ with $\mathrm dW = p\,\mathrm dV + \mathrm dW_\mathrm{el}$

$\mathrm dH = \mathrm dU + p\,\mathrm dV + V\,\mathrm dp \tag{2}$

Substituting (2) in (1):

$\mathrm dH - p\,\mathrm dV -V\,\mathrm dp = \mathrm dQ - p\,\mathrm dV - \mathrm dW_\mathrm{el} \tag{3}$

with $\mathrm dp=0$ follows:

$\mathrm dH = \mathrm dQ -\mathrm dW_\mathrm{el}$, differentiation with respect to time:

$$\frac{\mathrm dH}{\mathrm dt} = \frac{\mathrm dQ}{\mathrm dt} - \frac{\mathrm dW_\mathrm{el}}{\mathrm dt} = \dot{Q} - EI$$

So far, everything is fine. But now:

$$H = G + TS \rightarrow \frac{\mathrm dH}{\mathrm dt} = \frac{\mathrm dG}{\mathrm dt} + T\,\frac{\mathrm dS}{\mathrm dt} + \frac{\mathrm dT}{\mathrm dt}S$$

Here my first problem in understanding arises: In general $\frac{\mathrm dG}{\mathrm dt}$ and $\frac{\mathrm dT}{\mathrm dt}S$ cancels each other, since, $S=-\frac{\mathrm dG}{\mathrm dT}$ and $\frac{\mathrm dG}{\mathrm dt}$ can be expanded with $\mathrm dT$: $\frac{\mathrm dT}{\mathrm dt}S = -\frac{\mathrm dT}{\mathrm dt}\frac{\mathrm dG}{\mathrm dT}$. This means, that the influence of the open circuit voltage in the given energy balance would vanish.

I assume, that this is prevented by simply stating isothermal conditions: $\frac{\mathrm dT}{\mathrm dt}S = 0$. But this makes no sense to me, since the whole purpose of this calculation is the temperature increase with time during cycling a cell. Can somebody explain this to me?

Now if $\mathrm dT=0$ the derivation would proceed like this:

$$\frac{\mathrm dG}{\mathrm dt} + T\,\frac{\mathrm dS}{\mathrm dt} = \dot{Q} - EI$$

$$\frac{\mathrm d(-znFE_0)}{\mathrm dt} + T\,\frac{\mathrm d\left(znF\,\frac{\mathrm dE_0}{\mathrm dT}\right)}{\mathrm dt} = \dot{Q} - EI$$
where $znF=C$ is the charge and $\frac{\mathrm dC}{\mathrm dt} = I$

And here my second problem arises: to get to the equation at the very beginning of this post, it is necessary to set $E_0$ and $\frac{\mathrm dE_0}{\mathrm dT}$ constant, so that the chain rule does not apply. And I do not understand why this should be valid?

Can anybody help me with this?


texts: How does composition of air affect vapor saturation limit?

texts:
Suppose we hold temperature, pressure, and gas composition (say, a standard atmosphere) constant.  Then we know that if we allow the water content of the air to vary it can range between 0 and some saturation limit S g/L.

How does that saturation limit vary with the composition of the air?  For example, does it depend on the molecular weight and proportions of the other constituents of the air?

Assuming the water (or whatever substance is in question) does not chemically react with any other constituents at that temperature and pressure are there other constituent chemical relationships that can affect the saturation limit?


texts: Bromine radical reaction with an alkene - What factors determine whether radical addition occurs as oppose to radical abstraction?

texts:
From what I can tell, radical addition occurs when using HBr + Organic peroxides as reagents, and radical abstraction occurs when using trace amounts of bromine radicals (generated by NBS, trace HBr and UV).

However, in the end, a bromine radical is reacting with an alkene. Why / how do the preceding reagents determine the regioselectivity of the radical reaction?


texts: How do I name a molecule with a compound substituent?

texts:
I added a branch to the example shown in the textbook. What do you do when your longest carbon chain has a $\ce{CH2Cl}$ attached to a certain carbon?

Previously the book treated it as a methyl group and a halogen but my modification changes the length of the longest carbon chain so how do I name this molecule?

I think it is named 5-chloromethylheptan-3-ol.


texts: The major product of 1,4-pentadiene NBS bromination

texts:
Considering penta-1,4-diene, if allylic substitution is done with NBS, which product will be major, 3-bromo or 1-bromo?
In the first case I get stable free radical , in the second case I get conjugated diene.
Should I consider stability of free radical first as it is formed first , or the stability of the product which is formed in the end?


texts: Why are multiple extractions better than a single extraction?

texts:
I'm extracting $\ce{N-(4-butoxyphenol)-N'-(4-dimethylaminophenyl)thiourea}$ from thiombutosine (anti-leprosy drug) tablets. I'm doing this extraction with hot ethanol.

My question is why are 4 successive 10mL extractions better than a single 40mL extraction?


texts: How does one experimentally determine virial coefficients?

texts:
The Virial expansion is a systematic correction to the ideal gas law which takes the form of an expansion around the number density, $\rho$, of the gas in question. It looks like this: $$\frac{p}{k_bT}=\rho+B_2(T)\rho^2+B_3(T)\rho^3+\cdots$$
The form of this equation is not surprising. An ideal gas is simply one for which the coefficients $B_2$, $B_3$, etc. are equal to zero. These are called the second and third Virial coefficients.

According to Wikipedia (and I have heard this elsewhere), the Virial coefficients systematically correct the ideal gas law by considering specific interactions. To quote the Wikipedia article,

  The second virial coefficient $B_{2}$ depends only on the pair interaction between the particles, the third ($B_{3}$) depends on 2- and non-additive 3-body interactions, and so on.

This quote gives me quite a good idea of how I would determine these coefficients theoretically using $\textit{ab initio}$ calculations, but I can't imagine how I could calculate only the 2-body interactions experimentally...

Indeed, this paper seems to present one way to determine them by the so-called Burnett method, but I don't have a way of accessing this paper and have never heard of this method.

So, if anyone could give me a summary of how to determine these coefficients, I would appreciate that and am quite interested to hear the answers.


texts: Potassium bicarbonate or sodium bicarbonate

texts: How would I go about determining whether a sample of an unknown substance is either potassium bicarbonate or sodium bicarbonate (given that the sample is one or the other)?


texts: Why can't Pd/C and H2 reduce both the alkene and carbonyl portions of α,β-unsaturated carbonyls?

texts:
Why is it that the major product of the reduction of chalcones the ketone and not the monoalcohol? In other words, Why isn't the major product a benzyl alcohol?

From what I understand, catalytic hydrogenation can be used to reduce carbonyls as well as alkenes.

My TA told me that nucleophilic hydrides are preferred for reducing carbonyls. Why wouldn't hydrogenation work as well? Does it have to do with resonance involving the carbonyl since in a chalcone, the carbonyl is adjacent to an aromatic ring and is also conjugated with the alkene? Could the reason that catalytic hydrogenation can't effectively touch the α,β-unsaturated carbonyl be the same reason catalytic hydrogenation can't effectively reduce carboxylic acids, esters, and amides — all of which are also resonance stabilized?

My first thought had to do with heats of hydrogenation and how resonance-stabilization found in carboxylic acids and its derivatives reduce the heat of hydrogenation. However, later I found a resource online implying that all pi bonds - even the delocalized, resonance-stabilized ones found in benzene — could be reduced through catalytic hydrogenation with enough time.

In addition, it was noted elsewhere that chalcones could be completely reduced to the benzylic alcohol, although not with ease.

This leads me to believe that there is an activation energy barrier that's impeding the hydrogenation of certain substrates within the confines of a 3 hour undergraduate lab period … am I on the right path? Sterics, perhaps? It was noted that the more highly substituted an alkene is, the slower it is reduced because of the difficulty in getting a highly substituted alkene to approach the catalyst's surface with the $\ce{M-H}$ bonds in an appropriate manner.


texts: Why does the quantum number n limit the value of l, and why does l, likewise, limit the value of m?

texts:
Any quantum number that represents the size of an orbital is a positive integer, $n$.
Any quantum number that represents the shape of an orbital is a non-negative integer, $l : l < n$.
Any quantum number that represents the orientation of an orbital, $m$, is an integer such that $|m| \leq l$.

Why do $n$ and $l$ restrict the ranges of $l$ and $m$, respectively?

To be clearer, I ask why the quantum numbers limit each other, not what they signify, which is already explained in the related question: What do the quantum numbers actually signify?


texts: Why is Cadmium so carcinogenic compared to other heavy metals?

texts:
This free article as well as this article do a good job highlighting the carcinogenic effects of Cadmium and the mechanisms by which they occur. However, my question is why is Cadmium so carcinogenic compared to other heavy metals? What chemical property of Cadmium makes it more prone to these carcinogenic actions than, say, Mercury or Lead or some other heavy metal?

To give a more concrete example, the recommended safe levels of Lead in water is 50 ppb, whereas for Cadmium, it is 5 ppb. Why is there such a stark difference in their health effects?


texts: What is the name and formula of this structure?

texts:
Could anyone please let me know the formula and name of this structure? Any answer is helpful. Could you also summarize how to deduce the formula?

Here is an image:


texts: Converting bromobenzene to 1‐bromo‐3‐methylbenzene

texts: I started by taking $\ce{FeCl3}$ to reduce electron-giving capacity of $\ce{Br}.$ Then we need a methyl at meta, so I thought about Friedel–Crafts acylation, but then also methyl will come at para.


texts: Will water interfere with an in-situ XAS measurement of the Pt L3 edge during OER on a water electrolysis cell?

texts:
I am trying to design a cell for an in-situ experiment. As much as possible, I was hoping to be able to do it on a PEM MEA rather than on a half cell immersed on an electrolyte. I am thinking that water will likely interfere with the measurement during transmission mode so I am trying to think of ways to work around it.
However, I was looking at other works reported in literature and it seems that water interfering with the measurement is not being mentioned and they are more concerned with the bubbles. So this got me to wonder, is the effect of water really that significant after all? Or can I minimize it by simply "thinning" out the part of the chamber of the cell containing water which the X-ray will pass through?


texts: Phenol preparation from Grignard reagent

texts:
Reaction: Phenyl magnesium bromide in presence of excess oxygen, on acidification yields phenol, as below.

My instructor told me that the above reaction occurs, and if the reagent is in excess then phenol is the end product. However, I'm not able to figure out the mechanism.

I've tried and got stuck at this point:

I wish to know the complete mechanism of this reaction.


texts: The need for excess acid in dehydration of alcohols

texts: Why is there a need to use excess acid in the dehydration of alcohols? My instructor said that excess acid is necessary to minimize the ether formation via the competing SN2 mechanism, but I'm not sure how this works.


texts: Is it possible to have a diatomic molecule of sodium in gaseous state?

texts: Already I know that hydrogen, all the halogens, nitrogen and oxygen forms diatomic molecules. But I am confused about $\ce{Na}$? So I would like to know about that.


texts: Why are signals broadened in polarography?

texts:
In the attached polarogram from Heyvrovsky's 1959 Nobel lecture, transitions from one plateau to the next are smoothened out rather than sharp and abrupt. Why is that?

I understand that currents were small in this experiment, so metal ion concentrations should not change significantly.

I would have expected the current to jump from one level to the next as soon as the necessary voltage is reached. What broadens these transitions?

https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1959/heyrovsky-lecture.pdf


texts: NMR Splitting for Adjacent, Equivalent Hydrogens?

texts:
Why don't chemically equivalent hydrogens on adjacent carbons split the 1H NMR signal? There appears to be an answer here, but I'm having trouble understanding it because I cannot rationalize what happens with the magnetic field.

Let's say we're analyzing acetylene. When we subject the molecule to an external B-field, both (equivalent) protons have 2 possible spin states. For each proton, I would expect that the other proton's magnetic moment may either augment or oppose B0, causing a doublet. When we look at the signal for the other proton, it's the same story--I would expect 2 peaks identical to the 2 for the first proton (effectively doubling the integration).

Where have I gone wrong in extending spin-spin coupling to identical hydrogens? Why does the magnetic moment of adjacent, equivalent protons not affect the transition energy?

Edit: I asked my organic chemistry professor this question, and his response was that there does exist spin-spin coupling of identical protons, but the coupling constant is equal to 0. The reasoning involved quantum mechanics that went over my head.


texts: Direction of valence bond and Unsöld's theorem

texts:
Is it true that the atomic orbitals of separate atoms already have directionality, which ensures the directionality of the valence bond? Or another words, what is the real spatial distribution of the electron density in the atom, obtained in the one-electron approximation?

Doesn't this contradict Unsöld's theorem that states the square of the total electron wavefunction for a filled or half-filled sub-shell is spherically symmetric?


texts: How does temperature affect the concentration of flavonoids in orange juice?

texts:
I am in high school, and I would like to do an experiment on this for a project.

I've done quite a bit of research into the different methods I could use (see 2.4.2 here) but I still cannot find enough information to formulate a hypothesis. It would be useful iff you could point me in the right direction. So, how does heat affect how much flavonoids are present in commercially available orange juice? (without pulp)


texts:
I am learning about carbonyl chemistry at the moment. So far, we have been able to make aldehydes and ketones from alcohols (via oxidizing agents). I can't help but wonder if there is possibly any way to make aldehydes from ketones or vice-versa through a series of synthetic steps. I would appreciate it if the synthetic steps are in the level of an undergraduate organic chemistry course.

Question: Synthetic steps for the interconversion between aldehydes and ketones?


texts: Multiple bonds solely with sp3 hybridised orbitals?

texts:
I have fond that similar question has been asked already (why don't carbons use sp3 instead of sp2 orbitals to make double bonds?), but I don't think it was formulated in a manner that was touching the concept I am interested in.

I would like to know is it reasonable to consider double and triple bonds as result of overlapping solely sp3 hybridised orbitals. I imagine that alternative view on carbon-carbon double bond in ethene could be that two pairs of sp3 hybridised orbitals from each carbon overlap - giving four molecular orbitals, two of which would be bonding and fully occupied while other two would be empty. Moreover, geometry of such constructed double bond would be correct as all four hydrogen atoms bonded by remaining four sp3 orbitals from the two carbons would be coplanar (together with these two carbon atoms as well) and length of the bond would also be shorter than for single bond. I believe that similar case could be made for carbon-carbon triple bond.

Below I am presenting you a simple figure I have made to graphically demonstrate the idea.

I do recall seeing this concept is some textbook being presented as legitimate thing, I do not remember where it was, unfortunately.

Could you please explain it to me if this concept is reasonable idea, and if not - then why not? It would also be great to know how does energetic levels in such instance compare to the system with multiple bonds created by overlaps including hybridised and nonhybridized orbitals. (The one thing that appears in my mind is that in commonly accepted version of multiple bonds there is sigma bond that has electron density directly between nuclei making this arrangement more favourable. However, there are systems like two electron three centre bonds, as in B2H6, in which three centres are hold in similar arrangement to discussed above)


texts: Are there different types of melamine resin?

texts:
Background

I have a little knowledge of chemistry.

I was talking to a sales rep from a cleaning supplies company. They sell a scrub sponge that looks and functions just like Mr. Clean Magic Eraser. The sales rep was trying to scare me by saying that magic erasers have formaldehyde.

I know that the properties of a chemical compound are different than the properties of each component. I suspected that their product is actually the same as the magic eraser so I contacted the company directly, but got a less than satisfactory answer.

I asked if their sponge was made of formaldehyde-melamine-sodium bisulfite copolymer. They did not answer yes or no. They told me their sponge is made of melamine resin.

According to Wikipedia, melamine foam (a foam-like material consisting of a formaldehyde-melamine-sodium bisulfite copolymer) is a special form of melamine resin that is used mainly as an insulating and soundproofing material and more recently as a cleaning abrasive.

I would like to be more knowledgeable next time this sales rep contacts me. Hence the question.

Questions

Is there another way to make an abrasive foam sponge out of melamine resin that is not formaldehyde-melamine-sodium bisulfite copolymer? Is there a way to make a melamine resin without using formaldehyde?


texts:
A book which I am reading has this topic on hydrolysis of salts.
Suppose $\ce{NH4Cl}$ is dissolved in water. It is a salt of a strong acid and a weak base. $\ce{NH4+}$ ions being the conjugate acid of a weak base is strong and reacts with $\ce{H2O}$ to give $\ce{H+}$ thus making the solution acidic.
$$\ce{NH4+ + H2O <=> NH4OH + H+}$$
Now for calculating degree of hydrolysis $h$ it takes the initial concentration to be $C$. This means $C(1-h)$ of $\ce{NH4+}$ remains and $Ch$ each of $\ce{NH4OH}$ and  $\ce{H^+}$ is formed. Therefore, $K_h = \frac{Ch^2}{1-h}$. In the next step $1-h$ has been approximated as $1$. While calculating degree of dissociation of weak electrolyte we do a similar thing but that is because degree of dissociation is too small compared to 1 but here, I cannot understand how can degree of hydrolysis be very small compared to 1 when $\ce{NH4+}$ is a strong acid.


texts:
The pH of pure liquid water depends on temperature. It is about pH = 7.0 at room temperature, pH = 6.1 at 100 °C, and pH = 7.5 at 0 °C. What happens to the pH (or to the ion product) of pure water when it freezes?

I assume that the proton transfer reactions
$$\ce{2H2O <=> H3O+ + OH-}$$
$$\ce{H3O+ + H2O <=> H2O + H3O+}$$
$$\ce{H2O + OH- <=> OH- + H2O}$$
are too fast, so that any present $\ce{H3O+}$ and $\ce{OH-}$ cannot be easily trapped in the solid ice crystal when it grows. Does that mean that pure ice crystals are free of $\ce{H3O+}$ and $\ce{OH-}$ ions?


texts:
How does heptafluoropropane suppress fire?

It says here that it does so by "inhibiting the chain reaction."  What does that mean specifically? Does $\ce{O2}$ attach itself to the heptafluoropropane?


texts: Using solubility product to determine the mass of the precipitate of a reaction

texts:
I mix together $\pu{100 mL}$ of an aqueous $\ce{NaCl}$ solution at $\pu{0.5 M}$ and $\pu{100 mL}$ of an aqueous $\ce{AgNO3}$ solution at $\pu{0.3 M}$. Assuming that the solubility of $\ce{NaCl}$ in water is $\pu{360 g/L}$, the solubility of $\ce{AgNO3}$ in water is $\pu{2340 g/L}$, the solubility of $\ce{NaNO3}$ is $\pu{921 g/L}$ and the $K_\mathrm{sp}$ of $\ce{AgCl}$ is $1.77 \times 10^{-10}$, what is the mass of the precipitate ($\ce{AgCl}$) formed?

I know that the answer to this problem is $\pu{42.1 g}$, I solved it using stoichiometry. However, I want to know how to solve it using the solubility product and the other solubility figures given.


texts: I was reading about the atomic orbital in my chemistry textbook. It says that the atomic orbital (psi) is a mathematical wave function that depends on the coordinates of the electron. It is also mentioned that psi does not carry any physical meaning. That part is understood, however I could not understand what a psi vs r graph represents.(r is the distance from the nucleus) Can someone please clarify ??


texts: Can oxidation of ethanol by copper(II) oxide yield copper(I) oxide as one of the products?

texts:
We know that ethanol is oxidised by copper(II) oxide to an aldehyde. Copper is reduced from $\ce{Cu^2+}$ to $\ce{Cu}$. Can this reaction, with some specific condition, yield $\ce{Cu2O}$ instead? That will also be a reduction of copper, only partial.

The question was asked on a Russian chem forum and it made me curious.


texts: Does hydrogen peroxide exhibit intramolecular hydrogen bonding interactions?

texts: We know that intermolecular hydrogen bonding is seen in hydrogen peroxide $(\ce{H2O2})$. But is intramolecular H-bonding, i.e. hydrogen bond between an oxygen atom and a hydrogen atom attached to the adjacent oxygen atom possible? How strong will it be, compared to intermolecular H-bonding and why?


texts: Why does enantiopure sec-butyl alcohol retain its optical activity over aqueous base but forms a racemic mixture over dilute sulphuric acid?

texts:
Why does enantiopure sec-butyl alcohol retain its optical activity over aqueous base but forms a racemic mixture over dilute sulphuric acid ?

My reasoning is that, sec-butyl alcohol get dehydrated into a alkene because of sulphuric acid and then get hydrolysed to form alcohol again. Thus a equilibrium is formed between alkene and alcohol and between $R-$ and $S-$ sec butyl alcohol.
Dehydration cannot occur with a base, so the alcohol remains optically active.

I feel that conversion of alcohol to alkene and then back to alcohol seems ridiculous and impossible. What do you think, is this reasoning correct or just plain non-sense ?

To be specific, I have some doubt whether alkene will convert back to alcohol or not in dil sulphuric acidic ?


texts: What would be the 19-F decoupled proton NMR of this complex [PtH(PF3)4]-?

texts:
The proton is in the equatorial position and the geometry of the complex [PtH(PF3)4]- is trigonal bipyramidal.  The NMR is 19-F-decoupled proton NMR.

My thoughts were that the proton would couple to the platinum centre, but then I wasn't sure about the phosphorous chemical environments.

Are the two axial PF3 groups in a different chemical environment to the two equatorial PF3 groups?

If so would you end up with 6 sets of triplets? Is that a doublet of triplet of triplets?


texts: Inability of alkyl fluorides to be reduced to an alkane in the following reaction

texts:
Alkyl halides except fluorides on reduction with $\ce{Zn}$ and dil. $\ce{HCl}$ gives alkane. Example:

$$\ce{CH3Cl + H2 -> CH4 + HCl}$$

Why cannot alkyl fluorides be reduced?


texts: Why is the second acid dissociation constant for sulphuric acid much lower than the first in water?

texts:
In aqueous solution, $\ce{H2SO4}$ ionises in two steps :

$$\ce{H2SO4(aq) -> H+(aq) + HSO4-(aq)}; \quad K_\mathrm{a_1}=1\times10^3$$
$$\ce{HSO4-(aq) -> H+(aq) + SO4^2-(aq)}; \quad K_\mathrm{a_2}=1.2\times10^{-2}$$

The value of $K_{\mathrm{a}_2}$ caught my attention. I thought that $\ce{H2SO4}$ was a strong dibasic acid, but a very low value of $K_{\mathrm{a}_2}$ implies that the second proton is not that easily donated. Why is the value of $K_{\mathrm{a}_2}$ so less?


texts: Reaction of Rubidium with vacuum system viewport

texts:
I have a vacuum system ($<1\times10^{-7}$ mbar) filled with Rubidium ($^{87}$Rb) vapour, at room temperature.

We also have a viewport near the Rubidium source, made of a stainless steel flange and a glass substrate, connected with a Kovar alloy.

We are seeing potential degradation of the seal, which we do not see on other parts of the system. The only difference is the Nickel and Cobalt based Kovar alloy, not present anywhere else.

What are the reaction rates of Nickel and/or Cobalt with Rubidium?


texts:
A $\pu{3.45 g}$ piece of marble ($\ce{CaCO3}$) is weighed and dropped into a beaker containing $\pu{1.00 L}$ of hydrochloric acid. The marble is completely gone $\pu{4.50 min}$ later. Calculate the average rate of reaction of $\ce{HCl}$ in $\pu{mol/L/s}$. Note that the volume of the system remains at $\pu{1.00 L}$ through the entire reaction.

I'm not very sure why the units are in $\pu{mol/L/s}$ instead of just $\pu{mol/s}$. Here is what I did:

$$\text{Rate} = \frac{\pu{3.45 g}~\ce{(CaCO3)}}{\pu{4.5 min}} = \pu{0.0128 g/s}$$

$$\pu{0.128 g}~\ce{CaCO3} = \pu{1.28e-3 mol}$$

$$n(\ce{HCl}) = \pu{2.58e-3 mol}$$

$$\text{Rate} = \pu{2.58e-3 mol/L/s}$$

However, the answer given is $\pu{2.55e-4 mol/L/s}$. What am I doing wrong?


texts: Spectroscopy and Excitation of Electrons

texts:
As metals are heated, they glow white and then blue. How might you explain this change in color as the temperature of the metal is increased?

My answer consist of the idea that with increased thermal energy more electrons are excited and as they decay they emit wavelengths of the color blue. I am not sure how to connect the idea of white light to this answer because white light consist of all the wavelengths of the visible spectrum.


texts: Data-processing pipeline for protein x-ray crystallography: uncertain of terminology and order of procedures

texts:
Background: I am trying to get an overview of the data-processing pipeline for solving protein structures by x-ray crystallography, and in a very simple way understand what mathematical procedures are conducted at what step of the processing pipeline. I find data-processing a bit confusing as both textbooks and information on the internet seem to either give very basic explanations or way to technical (i.e. mathematical) explanation (and crystallography also seems to be full of confusing jargon terminology). Or alternatively, the information is focused on “clicking” you way through technical programs to produce an electron density map (which is great!), but without really explaining what the main steps of data processing consists of i.e. why you are doing them.

I would appreciate some clarification/confirmation that I have understood the overall process correctly. I can "click my way through" programs such as XDS/ Aimless/ Pointless/ Ctruncate/ MolRep/ Buccaneer and then finally work in coot for model in the electron density map. However, I don’t really understand the steps (in the data processing), a lot of it is simply just "click this" then "click that".

Specification of question: Everything up to the point of getting a protein diffraction pattern is okay, and everything after the electron density map is generated - is also okay. It is specifically the part between diffraction pattern and electron density map that is a bit confusing (also in terms of terminally used to explain the processing).

My perhaps error-prone understanding so far:

The diffraction pattern (collected at 360 degrees) of a protein crystal represents the reciprocal lattice.

The reciprocal lattice is an abstract concept for mathematical calculations, and does not represent the real crystal which exists in what is referred to as “direct lattice”, “crystal lattice” or “real space” (they are all the same thing?). The reciprocal lattice exists in reciprocal space (which is also referred to as k-space in physics?).

We can index the spots of the reciprocal lattice to generate miller indices(hkl) for each spot.

By indexing the intensities of the spots on the reciprocal lattice, we can determine the amplitude of the waves that diffracted from the crystal, but they do not contain any information about the phases of the wave relative to each other. This is the part where braggs law is used (i.e. a part of indexing?)

We then scale and merge reflections

Merging is grouping together identical reflections which increases the multiplicity of the data set (i.e. a good thing for statistics). Scaling is a bit abstract, and I know it is done in programs such as XDS during indexing (or right after indexing) and it somehow places all the reflections on a common scale.

We need to determine the structure factors (F) that contain information of the phases (or is this done at an earlier step, or at several steps of the process?)

This has to be done my molecular replacement or other methods (i.e. to solve the phase problem)

Assuming we use molecular replacement to solve the phase problem, are we then using the Patterson method of solving the structure?

After determining the phases, we can generate an electron density map is in “direct space/real space” by performing an inverse Fourier transform from the frequency domain to the time domain (f(t))? (or is it opposite, i.e. “normal” Fourier transform?)


texts: Experimenting with electrochromic prussian blue

texts:
I am attempting to preform this experiment. Chemistry isn't really my cup of tea, so I have a couple questions.

The instructions say to provide 40µA per cm2, where does that number come from?

The TIO material I'm using has a different resistance than the glass listed, will that change anything?

All the pt wire I could find was very pricy so I though I would use a graphite electrode instead, but all I can find is carbon electrodes. Is that close enough?

Here is the list of materials I have come up with, let me know if any of them are wrong.

HCI
Potassium Ferricyanide
Iron III
KCI
ITO Plastic
Carbon Flat Electrode This was much larger than I thought. Will the size be fine, or should I find a smaller electrode?

Thank you! I'm really excited about attempting this, hopefully I can pull it off.


texts: How to convert a linear dicarboxylate species to the dimethyl ester?

texts:
I was wondering about the ozonolysis of cyclohexane and further treatment with $\ce{H2O2}$. I understand that the product to this reaction is hexanedioic acid.

How could we substitute the $\ce{-H}$ on each carboxylic group to a methyl, as in the following structure:

I am pretty sure it would be by adding two moles of methanol (Fischer esterification). Is this procedure correct?


texts:
First of all. I am really bad at chemistry and all that. So this might or more likely will sound at least primitive... But this question has been bothering me for far too long.

So, I was reading about an atom. How all different kinds of it differ by the number of protons in its nucleus. And that gave me this utopian thought: maybe in far (like, really far) future we will have some sort of super "printers" which could take anything as their "ink" and somehow turn that anything (a brick for example) into manageable atoms.

Then it probably should identify each atom, by counting its protons and edit it by "deleting", "adding" or separating needed number of the protons and neutrons.

So my question is... Do you think this is theoretically possible?
Are there any known ways of changing the number of protons?

*Edit: as it turns out, there is a talk going on about this kind of utopia: https://www.youtube.com/watch?v=RzgVWpa4fzU

Big thanks for your answers! I wasn't expecting to receive any answers :)*


texts: How to get the efficiency of a heat engine which undergoes an elliptical cycle?

texts:
An ideal diatomic gas undergoes an elliptic cyclic process characterized by the following points in a $PV$ diagram:
$$(3/2P_1, V1)$$
$$(2P_1, (V1+V2)/2)$$
$$(3/2P_1, V2)$$
$$(P_1, (V1+V2)/2)$$

A rough sketch:

This system is used as a heat engine (converting the added heat into mechanical work).
Evaluate the efficiency of this engine

We know that the efficiency is defined as the benefit/cost ratio:
$$e = \frac{W}{Q_h}$$
Let's focus first on the work done by the engine; taking into account the quasistatic approximation, $W=PV$. Then:
$$W = (P_2 - P_1)(V_2 - V_1)$$
Note that from the given points we can guess that $P_2 = 2P_1$. Then:
$$W = P_1(V_2 - V_1)$$
Now let's focus on $Q_h$. I have the following issue here: none of the 4 steps of the cycle has either P or V constants. This means that the strategy of using:
$$Q = nc\Delta T$$
Won't work because you cannot use neither $c_p$ nor $c_p$.
However, when we deal with a rectangular cycle:

It would be really easy to derive expressions for both $Q_a$ and $Q_b$ and then the efficiency for the system would be obtained. That is because in each step $Q_h$ is added, either $P$ or $V$ are constant (and thus $Q = nc\Delta T$ works).
What to do with the elliptical cycle to get $Q_h$?
EDIT
My bad, the work done by the working substance is the area under the PV graph. So as Chet Miller pointed out, the work is:
$$W = \pi (P_2 - P_1)(V_2 - V_1)$$
I have been trying to solve the heat equation so that we get the two angles.
So what I did was deriving $P$ and $V$ wrt the angle:
$$dP = (P_{max} -P_0)\cos \theta d\theta$$
$$dV = (V_{max} -V_0)\sin \theta d\theta$$
And plugging it into 3:
$$0=[-(C_v+R)P(V_{max} -V_0)\sin \theta+C_VV(P_{max} -P_0)\cos \theta]$$
This above equation is satisfied by two $\theta$ angles. But how to solve it?


texts: Can Pyrex laboratory grade glassware be heated on a stovetop?

texts: I don't have access to a hot plate, I was wondering if Pyrex glass can be safely heated on a stove top. It isn't an open flame, it's a radiant stove top with an electric coil underneath a smooth counter. I believe the heating should be even because the coil heats the entire stove top evenly.


texts: How much glucose oxidase is usually deposited on a glucometer strip?

texts:
The concentration of serum glucose is on average roughly around 5 mmol/L and let's say a typical blood droplet applied to a glucometer is 1μL. We are therefore depositing 5 nmol of glucose on the test strip.
  These 5 nmol of glucose interact with the enzyme glucose oxidase and through a redox mediator a current is measured. This current is proportional to the concentration of glucose present and it is in the order of few μA (see Figures below taken from Ref.1 and 2). Each glucose molecule is oxidased to glucono-lactone by the enzyme glucose oxidase releasing 2 electrons to the amperometric circuit; that means that if we have 5 nmol of glucose, then 10 nmol of electrons are released or equivalently around 1 mC:
$$Equation 1: \frac{10*10^{-9}mol*6.022*10^{23}electron/mol}{6.24*10^{18}  electron/C} ≃ 1 mC $$

Once the oxidation of glucose starts, the current measured increases reaching its maximum for few seconds (time-frame of maximum stability) and then decays. The current used to calibrate and measure the concentration of glucose is taken during this stable time-frame of maximum current.  If the current measured is of few μA (i.e. let's say 10 μA), that means that in 4 seconds (I have read 2-4 s is typical), only 40 μC (or 0.04 mC) are released and this accounts for 4% of the total number of electrons that would be released if all the glucose contained in the blood droplet is oxidised (see equation 1).
 1.Does it mean that usually less than 10% of all glucose is effectively oxidised? if yes, why? What are the main factors that limit the yield so much?

It is also very difficult to find data on how much glucose oxidase is deposited on the strip. If the max current is roughly around 10 μA that means that 10 μC (or $6.24*10^{13}$electrons or ~ 0.1 nmol of electrons) are released every second; this means that 0.05 nmol of glucose are oxidised every seconds.
 Glucose oxidase can be considered to follow a Michaelis-Menten law:

$ Equation 2:  v = Kcat*[E_0]\frac{[S]}{Km+S}$, with $[E_0]$ the concentration of the glucose oxidase and $[S]$ of glucose (substrate)

$Kcat$ can be estimated to be around 740 $s^{-1}$, and Km 18 mM (see ref.3); in this example $[S]$ was 5 mmol/L and the enzyme was oxidising at a rate of 0.05 nmol/s.
 If we consider that the initial volume of the blood droplet (1 μL) is largely preserved during its travel to the reaction area of the strip, then $v = 5*10^{-5}M/s$.
 From this approximate data and equation 2, $[E_0]$ can be estimated to be around 0.3μM; considering the volume of 1 μL, then there are around $3*10^{-13}$ mol of glucose oxidase deposited on the strip or 50 ng (multiplying by the molecular mass of glucose oxidase, 160 kDa).
 2. Is 50 ng a reasonable estimate? Does anyone know (approximately) how much glucose oxidase is deposited on a strip?

Volume 2019, Article ID 5948182, The Influence of Blood Glucose Meter Resistance Variation on the Performance of a Biosensor with a Gold-Coated Circuit Board, https://doi.org/10.1155/2019/5948182,

https://slideplayer.com/slide/5728209/
Isolation, purification and characterization of a novel glucose oxidase from Penicillium sp. CBS 120262 optimally active at neutral pH, https://doi.org/10.1016/j.pep.2006.09.013


texts: Tools for investigating hydrogen bonding

texts:
What would be the best tool to investigate local molecular organization in liquid mixtures due to hydrogen bonding?

For example, I might want to look at how water molecules hydrogen bond to PNIPAM vs with itself.

Qualitative analysis would be good (does one type of site preferentially hydrogen bond with a specific other site) but quantitative would be even better (enthalpy of h bonds and entropy  reduction due to local organization).

What is a good way to look into this?


texts: Using Beer-Lambert law to calculate light intensities

texts:
Supposing the mean absorption coefficient of seawater in the visible region is $\pu{0.8 m-1}$, calculate the depth at which a diver will experience half the surface light intensity.
I know that you have to use $A = -\log \left(\dfrac{I}{I_o}\right) = \epsilon cl$ but I'm not sure how to proceed


texts: Whenever I searched "$\ce{B12H12}$ Borane", I can't seem to find anything, and get met with only the dianion of $\ce{B12H12}$. Why doesn't $\ce{B12H12}$ exist on its own?


texts: Reaction of aqueous sodium carbonate with aluminum foil

texts:
Aqueous sodium hydroxide is known to react with aluminum foil in an exothermic, hydrogen-gas releasing reaction like $$\ce{2NaOH(aq) + 2Al(s) + 2H2O(\ell) → 2NaAlO2(aq) + 3H2(g)}$$

However, on youtube, it looks like someone was able to substitute NaOH with Na2CO3 and get a vigorous similar-looking reaction as well: https://www.youtube.com/watch?v=ggPWdwcsyqM

Which makes me wonder — did they also form $\ce{NaAl(CO3)2}$ as well? E.g., via
$$\ce{2 Na2CO3(aq) + 4Al(s) + 6H2O(\ell) -> NaAl(CO3)2(aq) + 3NaAlO2(aq) + 6H2(g)}$$

Or was sodium carbonate merely used as a source of NaOH, from $$\ce{Na2CO3(aq) + H2O(\ell) \rightleftharpoons NaHCO3(aq) + NaOH(aq) }$$


texts: Why do some periodic tables have 18 groups while others have 8?

texts: In school I have been taught about the periodic table with 8 groups, representing the number of electrons in the outer shell (with exceptions). But online almost all I can find is periodic tables with 18 groups. Why do both exist? (Is the one with 18 more modern?) What is the purpose of 18 groups?


texts: Is there a correlation between the susceptibility of a polymer to undergo hydrolysis and its melting point?

texts:
As per topic, I was wondering why the Tm of the polymers PGA, PLA and PLGA are in the following order. Does it correlate to their ability to undergo hydrolysis?

PGA>PLA>PLGA


texts:
I have read about charcoal being used to clean water before it is then boiled or mixed with a UV light stick. I have some questions about this:

  1) Does it have to be activated charcoal?

  2) Can I use normal charcoal from any old shop (in the UK) as I assume
  these days everything is synthetic or have added harmful chemicals?

  3) Can it purify irradiated water? Yes I am a huge Fallout 3 fan!

If there is anything else that I might not have thought of asking, or might be interesting, feel free to let me know :-).


texts: What is the percentage of d-tartaric acid in a mixture of d and l isomers?

texts:
Specific rotation for pure tartaric acid is $-12 ^\circ$. A mixture of d-l isomers is prepared which has a specific rotation of $+6^\circ$. What is the percentage of d-tartaric acid in a mixture of $d$ and $l$ isomers?

The pure tartaric acid must have been $l$-tartaric acid.

My attempt:

$$\frac{l-d}{l+d}=\frac{+6}{-12}=\frac{1}{-2}$$ So $d=3l$. Which implies $$\frac{d}{d+l}=\frac{3}{3+1}=0.75 $$

However the answer given in my textbook is $66.67 \%$. Most probably I didn't do any calculation error. So where did I go wrong?


texts: Just out of curiosity, can dust conduct electricity? The source of dust varies, is there any form of dust that can conduct electricity?


texts:
The square of the wavefunction gives probability density of finding an electron somewhere in the orbital.
The text I'm referring to says that the value of probability density is always higher than zero at any finite distance from the nucleus.
so if probability density cannot be zero, then what about nodes? Arent they regions where probabilty density is zero?


texts: A lot of confusion in 1st law of thermodynamics

texts:
My sir told me that Total energy of system = K.E + P.E in starting.
Then Change in energy = F(External force on body ) * displacement of walls.
Then from here , change in energy = W+q.
(Don’t understand how we reached till here )
This change in energy is also called change in  internal energy.
Then it should be equal to Kinetic + potential energy of the molecules inside the system that we are considering .
Q1 is that if it is equal to kinetic + potential energy, then in case of ideal gases.P.E = 0.So K.E will be equal to change in energy $\delta U$.
Q2 is that if it change in energy , then it should be change in kinetic energy as well right.
Ok then my sir also tells me that when a reaction happens in non ideal gas scenario , example of 1mole N2 + 3 mole H2 = 2mole NH3.Now my sir says , there will be a lot of potential energy here.So we can’t use the formula kinetic energy = q+w here.
When Na(s) in converted to Na(g) we consider , delta H of sublimation of Na and then potential energy change I.e internal energy change = Na+(g) + e. Is this internal energy change $\delta U$.
All these doubts arrived from this question.
Because here they ask for internal energy change , so does it mean that it is $\delta H_1$ + $\delta H_2$ + Internal energy of 1 + internal energy of 2.
I am sorry if this in not written in good manner but am so much in tension right now that I just gave out everything I knew


texts: When I dissolve sugar in my cup of tea/coffee, does it become a liquid?

texts:
When I dissolve sugar in my cup of tea/coffee, does the sugar go from being a solid to being a liquid?

Related: https://physics.stackexchange.com/questions/5562/what-keeps-the-sugar-suspended-in-the-tea


texts: How much water is required to dilute glacial acetic acid to given pH?

texts:
I have 100% acetic acid (glacial) with a pH of 2.4 and I want to know how much DM water is required to dilute the acetic acid and obtain a solution with a pH of 4.3.
As per observation 0.0001 M is equal to pH 4.3. So how can I implement this calculation using the Nernst equation?


texts: How to determine pressure and concentration of carbon dioxide in blood plasma?

texts:
A man suffering from untreated diabetes mellitus is admitted to a hospital. Doctors fear that his blood $\mathrm{pH}$ may have dropped because of ketoacidosis. Analysis of his blood reveals that $[\ce{HCO3-}] = \pu{16 mM}$ and $p_\ce{CO2} = 30.$ If $\mathrm{p}K_\mathrm{a}$ of $\ce{HCO3-}$ is $6.1,$ determine whether the patient runs a risk of acidotic coma. (Note: in plasma under physiologic conditions, concentration of $\ce{CO2}$ and $p_\ce{CO2}$ are related by the solubility constant for $\ce{CO2}$ in plasma which is $\pu{0.03 mM/mm Hg}.$

We use the Henderson-Hasselbalch equation, then

$$\mathrm{pH} = \mathrm{p}K_\mathrm{a} + \log[\ce{HCO3−}][\ce{H2CO3}]$$

Moreover, here $\mathrm{p}K_\mathrm{a}$ of $\ce{HCO3-}$ is given whereas the acid is $\ce{H2CO3},$ and also if we consider second dissociation that is $\mathrm{p}K_\mathrm{a2}$ then also it is wrong because $\ce{HCO3-}$ will dissociate into $\ce{H+}$ and $\ce{CO3^2-}$ so in this dissociation there is no relation of $\ce{CO2}.$  And also why solubility constant is given, how can we find out $\ce{CO2}$ from solubility constant?


texts: charge density as a measure of lattice enthalpy & polarizing power?

texts:
My official CIE A level textbook, and some mark schemes mention the following:

Ions with the same charge have a lower charge density if their radius is large. This is because the same charge is spread over a larger volume. A lower charge density weakens the electrostatic attraction and thus decreases the lattice enthalpy of an ionic lattice.

From a physics point of view, this can't possibly be right, can it? Modelling the ions as spheres, gauss' law/ shell theorem clearly state that for all points outside a shell/sphere (of uniform charge density), the spheres/shells are equivalent to point particles. Why should the volume of the ion have any affect on the attractive force? And what would, then, be the correct explanation for decreasing lattice enthalpy down the group?
moreover, charge density of an ion is  also said to affect its polarising power. The polarisibing power should depend on the electric field created by the ion which,again, doesn't depend on the size at all. If this too is wrong, why does Be have a greater covalent character than Mg?


texts: What happens when we connect a external emf (having emf greater than that of emf of a galvanic cell) to a galvanic cell?

texts:
I read a statement given in the book and I did not understand it

"If any external battery is connected whose emf is more than the emf of galvanic cell ,then it will act as Electrolytic cell"

Also can you please explain what happens if we connect a external battery having emf less than that of galvanic cell?


texts: Dependence of Osmotic Effects on Particle Size

texts:
van't Hof's equation for osmotic pressure is derived with the assumption, among others, that the particle size of the solute is comparable to the particles size of the solvent. It holds well so long as they are at least within an order of magnitude or two of each other -- but clearly it breaks down eventually, because you don't get much in the way of osmosis with a suspension of sand, or (to be silly) a handful of ball bearings.

I'm interested in the middle range, here -- in particular, I'm assuming there is a middle range, where particles contribute somewhat to osmolarity but at a lower rate than unity. Is there a decent derivation -- or a formula, I'd accept a formula but I'd prefer a derivation -- for the dependence of osmotic pressure (or potential, or otherwise closely related property) on particle size?


texts: When I stretch a rubber band, the fibers straighten out causing lesser randomness and more order. This should imply the entropy of the rubber band has decreased, but how does the entropy of the whole universe increase here? Does this mean a rubber band gets colder on stretching? I have seen an experiment where it gets hotter. Doesn't entropy of the whole universe increase only in spontaneous processes? Here I have to pull it hence its not spontaneous? In a nutshell, I'm really confused.


texts: How does conversion of a free radical to a carbonyl compound take place? Unsure about mechanism

texts:
Came across a question that talked about fragmentation of peroxyesters, about the peroxide linkage of course.
After the fragmentation of the peroxyester was done, it gave out three products (2 being free radicals, and the other being carbon dioxide)

One of the products(i.e. free radical), went under a reaction (with itself) and gave two products, one being another free radical and the other being a carbonyl compound. I am unsure about the mechanism.

Here's what I thought:
The single bond between the C1 and C2 will cleave in a homolytic manner. The (now) unpaired electron on C1 will combine with the unpaired electron of oxygen to form a $\pi$ bond. Also, the unpaired electron will remain on C2.

Why am I not sure about my reasoning? Because why would a homolytic cleavage take place between C1 and C2 after all?

Any hints or tips would be highly appreciated.


texts: Is tetraammine dichloro cobalt (III) an optically active compound?

texts:
Is
$$ \text{Co}[{(\text{N}{\text{H}}_{3})}_{4}{\text{Cl}}_{2}]$$
optically active? If so, write its stereo-isomers.

I know that for a compound to be optically active, it should rotate the plane of Plane Polarized Light, but is there a way to do this without experiment?
Thanks!


texts: Balancing the reaction equation for the oxidation of lead(II) sulfide with ozone

texts:
While I was reading about the chemical reactions of ozone, I came across this reaction.
$$\ce{PbS + 4O3 -> PbSO4 + 4O2}$$

Though the reaction seems well balanced, but when I attempted to balance it myself, I did this as $$\ce{PbS + 2O3 -> PbSO4 + O2}$$

I understand that there must be some reason that the 1st reaction is given in the book. I'm just not able to figure out why.

Can somebody give an explanation as to why is it so?


texts: What material can be used as scraper in a chemical reactor?

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I am having a 10L reactor built using SS316 for Plastic Pyrolysis.

TEMPERATURE : 550C

I would like a scraper to clean the char that forms on the reactor's inner layer.

Teflon scraper is available but it will not withstand 550C temperature.

So I am thinking about using flexible expanded graphite (Similar to graphite gland packing ropes) material. What do you think?

What other options do you suggest that I look into?


texts: A basic question about tetramethylammonium hydroxide --strong or weak?

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This is a follow-up to the question here.  There is an answer claiming that tetramethylammonium hydroxide (TMAH) is a suitable strong base that can be used instead of the usual alkalies to reach pH 14.  However, Wikipedia says that TMAH is only a weak base.

But, when I state this I get comments that other sources document TMAH as a strong base.  The other sources, however, just mention it in passing and do not offer direct proof.  Can anyone provide a reference that actually does settle this question?  Thanks!

Note: At the time the question was posed Wikipedia did make the weak base claim. It has since been edited, and it now appears that the edit is correct.  See the answers.


texts: Preparation of phosphate buffer of ph 7.4

texts: Can I make a phosphate buffer of pH 7.4 starting with phosphoric acid and then adding NaOH until the pH reaches 7.4. What are the disadvantages of using this method over sodium phosphates?


texts:
i read in my textbook that the energy diagram of moleculal orbits is different for atoms nitrogen and below them.
my question is which one of the energy diagrams to use in heteronuclear compounds like CO?


texts: How do you explain partial charges in molecules that have a dipole?

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For example if i have hydrogen and fluorine covalently bonded with each other, it would result in a polar molecule with the valence electrons being pulled closer to the fluorine than it is to the hydrogen. At some time the electrons will be at the fluorine end more often as it has higher electronegativity and thus making the hydrogen end partly positive. How does this work? If one electron is pulled to the fluorine end (the one that is shared), doesn't this just revert the hydrogen to its neutral state (as an element) and not be a partly positive charge?

Or does the electrons that are shared also including the lone pairs are going to orbit the shell of the other covalently bonded element, so that in some time there won't be any electrons in one end?


texts: Difference between relaxation and resonance leading to an absorption spectral feature?

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I need help understanding the physics behind this insightful comment below the question Does water really have strong EM absorption at 3 kHz in solid and 2 GHz in liquid? Why the huge shift?:

  Please note: This is a relaxation spectrum. The transitions do not come from a resonance (absorption, like in NMR, IR, etc.), but an applied electric field has a lossy (at low frequencies) or elastic (at higher f.) effect on some mode of molecular orientation of electrical dipoles in your sample.

The following comment links to https://en.wikipedia.org/wiki/Dielectric_spectroscopy which confirms this.

Both mechanisms can to a peak in the imaginary part of the dielectric permittivity at a certain frequency or energy, and at this point the slope of real part is steepest.

But is there a simple yet intuitive way to understand the physical difference between a spectral absorption feature due to a resonance process versus a relaxation process?


texts: Standards for drawing chemical molecules

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I'll preface this by saying I haven't had a chemistry class in 10 years and molecular structures are not my thing. But I'm submitting a revision to a journal paper where I need to include figures of molecules and I need to make sure I get it right so I don't get nit-picked apart for it.

Is there a standard/guide/list of rules for how to create chemical molecule figures like the one below?

I'm looking for a comprehensive list of rules but as an example of things I would need to know:

Should I include the carbon atoms in the ring drawing?
At what angle should the entire molecule be drawn (I've seen rigid-body rotated versions of the same molecule before)?

Rather than answering those specific questions, I'd like to know if anybody (IUPAC maybe?) has a standard for drawing these figures.


texts: How to to test the concentration of melatonin in a strong acid?

texts: If a small tablet of melatonin was coated with a substance to ensure a slow dissolution in water and was then placed in a strong acid, neglecting the limits imposed by maximum saturation, it would slowly but surely dissolve. I would imagine the simplest method for determining exactly how much has dissolved would be by testing its concentration, however the information available on the topic uses methods beyond my capacity to preform as a high school student. Is there any relatively simple method to determine the concentration?


texts: What are some technologies/biosensors for real time kinetic analysis of reactions?

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I am in a lab that has used surface plasmon resonance (SPR) and ELISA very heavily over the past few years, and we are thinking of getting a new machine. I'm wondering what other technologies exist for making similar measurements; particularly protein -protein/antibody-antiggen binding.

Octet in particular looks very different because rather than passing a flow of analyte over the ligand, it puts them together in a chamber, which I'm guessing allows the user to make much longer measurements, which could be really useful for measuring low affinities and low concentrations.

Also what are peoples experiences of different Biosensors?