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Ethylene has been used in storing potatoes for a while, see this [article][1]. In it, they address the puzzle of a ripening agent acting to prevent sprouting:
> Sprout suppressant properties of apple ‘vapours’ were first reported in 1932 and subsequently, ethylene and apple ‘vapours’ in 1933 (Elmer and Huelin, respectively). This was preceeded, however, by work demonstrating a ‘dormancy breaking’ effect of ethylene (Rosa, 1925). These apparently conflicting responses to ethylene were resolved with the publication of work showing both effects, but under different ethylene exposure conditions.
The mechanism of the different effects are largely unknown. The cited article (by the British Potato Council) gives some references. Potatoes treated with ethylene do have slightly different properties (they mention the color after deep frying), and there is ongoing research to get an overview of all the differences.
>[OP:] Chemically speaking, do we actually know the exact reason and the necessary conditions to make this work?
We don't know the exact reason, but there are companies who figured out to make this work in a warehouse under controlled conditions. I think on your shelf would be more difficult because you have no way of monitoring the ethylene concentration, so the apples might influence the potatoes in etiher way.
[1]: https://potatoes.ahdb.org.uk/sites/default/files/publication_upload/R279%20Research%20Review%20Ethylene.pdf |
Suppose salt dissolves in water according to the equation NaCl(s) -> Na(aq) + Cl(aq). Since the activity of solid salt is 1, adding salt shouldn't affect sodium and chloride ions at equilibrium. However, if I were to add salt to an unsaturated solution, the salt would dissolve and increase the ion concentrations. How is it possible for the activity of solid salt to be 1 if it affects equilibrium in this way? My only theory is that an unsaturated solution is not at equilibrium, but I'm not sure this is correct. |
If the activity of a solid is one why does adding salt to water increase the salt ion concentration? |
I recently [asked][1] a question about *why the heat of formation of organic radicals and positive ions decreases with their size and degree of branching at the radical or ionic site*. The user "Buttonwood" made the comment that **hyperconjugation** is one of the forms stabilising cations and radicals.
This begs two questions:
1. What is the reasoning behind why hyperconjugation increases the stability of cations and radicals, and therefore decreases the heat of formation? Point 3. of [this][2] section of the Wikipedia article for hyperconjugation says that "*the heat of formation of molecules with hyperconjugation are greater than sum of their bond energies and the heats of hydrogenation per double bond are less than the heat of hydrogenation of ethylene.*"; does this not imply that hyperconjugation increases the heat of formation of molecules?
2. Why does an *increase* in stability imply a *decrease* in heat of formation? To a novice who is ignorant on this subject such as myself, it would intuitively seem that greater stability implies an *increase* in heat of formation, since the molecule is more "stable" in its current form and therefore it takes more energy to affect changes in its structure?
I would greatly appreciate it if people would please take the time to clarify these points.
[1]: https://chemistry.stackexchange.com/q/129037/75460
[2]: https://en.wikipedia.org/wiki/Hyperconjugation#Effect_on_chemical_properties |
Ethylene has been used in storing potatoes for a while, see this [article][1]. In it, they address the puzzle of a ripening agent acting to prevent sprouting:
> Sprout suppressant properties of apple ‘vapours’ were first reported in 1932 and subsequently, ethylene and apple ‘vapours’ in 1933 (Elmer and Huelin, respectively). This was preceeded, however, by work demonstrating a ‘dormancy breaking’ effect of ethylene (Rosa, 1925). These apparently conflicting responses to ethylene were resolved with the publication of work showing both effects, but under different ethylene exposure conditions.
The mechanism of the different effects are largely unknown. The cited article (by the British Potato Council) gives some references. Potatoes treated with ethylene do have slightly different properties (they mention the color after deep frying), and there is ongoing research to get an overview of all the differences.
>[OP:] Chemically speaking, do we actually know the exact reason and the necessary conditions to make this work?
We don't know the exact reason, but there are companies who figured out how to make this work in a warehouse under controlled conditions. I think on your shelf would be more difficult because you have no way of monitoring the ethylene concentration, so the apples might influence the potatoes in etiher way.
[1]: https://potatoes.ahdb.org.uk/sites/default/files/publication_upload/R279%20Research%20Review%20Ethylene.pdf |
Recently I've been reviewing concepts belonging to the history of chemistry. But I came stuck at trying to understand a passage which I read from wikipedia entry (and which it seems has been mentioned in different sources). This is related with the law of reciprocal proportions.
It states as this:
> It took 615 parts by weight of magnesia ($\ce{MgO}$), for example, to
> neutralize 1000 parts by weight of sulfuric acid.
There's an [existing answer](https://chemistry.stackexchange.com/questions/42903/what-is-the-significance-of-law-of-multiple-proportions) which explains a similar concept (law of multiple proportions) but not specifically to Richter's.
From what I understood in the law of reciprocal proportions there is a set of three elements. Two of them react with a fixed amount of a third element. The ratio of these two elements is the same when they combine between.
For example:
When $63.5~\rm{g}$ copper combines with sulphur produces copper sulphide
$\begin{array}{lllll}
\ce{Cu}&+&\ce{S}&\rightarrow&\ce{CuS}\\
63.5~\rm{g}&&32~\rm{g}&&95.5~\rm{g}\\
\end{array}$
Conversely when those $63.5~\rm{g}$ of copper combines with oxygen produces cupric oxide.
$\begin{array}{lllll}
2\ce{Cu}&+&\ce{O_2}&\rightarrow&2\ce{CuO}\\
63.5~\rm{g}&&16~\rm{g}&&79.5~\rm{g}\\
\end{array}$
Therefore the proportion between the mass of sulphur and oxygen masses is:
$\frac{m_{\ce{S}}}{m_{\ce{O_{2}}}}=\frac{32}{16}=2$
When sulphur and oxygen combine together they make sulphur dioxide.
$\begin{array}{lllll}
\ce{S}&+&\ce{O_2}&\rightarrow&\ce{SO_{2}}\\
32~\rm{g}&&32~\rm{g}&&64~\rm{g}\\
\end{array}$
Then the proportion between these two becomes:
$\frac{m_{\ce S}}{m_{\ce{O_{2}}}}=\frac{32}{32}=1$
The latter is in proportion which is half of the first ratio. Hence follows the Richter law.
But how can I use this information to understand what it was mentioned in the paragraph from above? How is exactly related with equivalent weights?
The second part of the question arises from the fact, that would it be okay to state this?
In an hypothetical reaction between $A$, $B$ producing $C$ and $D$.
$\begin{array}{ccccccc}
aA&+&bB&\rightarrow&cC&+&dD\\
\textrm{1 eq gram of A}&&\textrm{1 eq gram of B}&&\textrm{1 eq gram of C}&&\textrm{1 eq gram of D}\\
\end{array}$
Becoming in
$\textrm{1 eq gram of A}=\textrm{1 eq gram of B}=\textrm{1 eq gram of C}=\textrm{1 eq gram of D}$
Would it be accurate to put it in that way?
or?
$\textrm{number of eq gram of A}=\textrm{number of eq gram of B}=\textrm{number of eq gram of C}=\textrm{number eq gram of D}$
where:
$\textrm{1 eq gram A} =\frac{\textrm{grams of A compound equal to the equivalent weight of A}}{\frac{\textrm{formula weight of A}}{\textrm{number of electrons transfered}}}$
which is different when considering moles:
$\begin{array}{ccccccc}
aA&+&bB&\rightarrow&cC&+&dD\\
\textrm{a moles of A}&&\textrm{b moles of B}&&\textrm{c moles of C}&&\textrm{d moles of D}\\
\end{array}$
where:
$\textrm{a moles of A}=\textrm{b moles of B}=\textrm{c moles of C}=\textrm{d moles of D}$
So, is what I wrote correct? How can I relate Richter's law of reciprocal proportions to the equivalent weights? How is it related with the paragraph from above? Perhaps does it meant to say that there is a definite amount of reagent which can react with a certain amount of sulphuric acid? Then why isn't it related more with the concept of limiting reagent rather than the equivalent weight? Can someone guide me on that? |
We might have a half cell consisting of the redox couple $Ag^+/Ag$, which for example's sake might be fixed to be at the cathode (i.e. undergoing reduction).
The reaction at the cathode is then
$Ag^+ + e^- \rightarrow Ag$
The standard electrode potential of the $Ag^+/Ag$ couple is $+0.80V$. I've seen the above reaction written as such:
$Ag^+ + e^- \rightarrow Ag \space\space\space\space\space\space\space\space\space\space\space \mathcal{E} = +0.80V$
I'm confused as to why we write this electrode potential next to the reaction, considering that the electrode potential of a redox couple is reasonably disjoint to the concept of the chemical reaction. Although, at the end of the day, the chemical reaction results in the interfacial potential difference which causes the electrode potential, $\mathcal{E}$ is a property of the electrode, not the chemical reaction.
Is it perhaps just because we want to write the equation of the reaction occurring at a certain electrode *and* the electrode potential of the electrode on the same line?
I'm aware that for associating potentials with written reactions, there exist two different conventions: European, where all reactions are labelled with the reduction potentials of the couple, and American, where oxidation reactions are labelled with the oxidation potentials of the redox couple and likewise reductions with reduction potentials. However, my question is why we need to attach the electrode potential to the chemical reaction in the first place! Thank you. |
Why do we write electrode potentials next to chemical reactions? |
We might have a half cell consisting of the redox couple $Ag^+/Ag$, which for example's sake might be fixed to be at the cathode (i.e. undergoing reduction).
The reaction at the cathode is then
$Ag^+ + e^- \rightarrow Ag$
The standard electrode potential of the $Ag^+/Ag$ couple is $+0.80V$ wrt SHE. I've seen the above reaction written as such:
$Ag^+ + e^- \rightarrow Ag \space\space\space\space\space\space\space\space\space\space\space \mathcal{E} = +0.80V$
I'm confused as to why we write this electrode potential next to the reaction, considering that the electrode potential of a redox couple is reasonably disjoint to the concept of the chemical reaction. Although, at the end of the day, the chemical reaction results in the interfacial potential difference which causes the electrode potential, $\mathcal{E}$ is a property of the electrode, not the chemical reaction.
Is it perhaps just because we want to write the equation of the reaction occurring at a certain electrode *and* the electrode potential of the electrode on the same line?
I'm aware that for associating potentials with written reactions, there exist two different conventions: European, where all reactions are labelled with the reduction potentials of the couple, and American, where oxidation reactions are labelled with the oxidation potentials of the redox couple and likewise reductions with reduction potentials. However, my question is why we need to attach the electrode potential to the chemical reaction in the first place! Thank you. |
We might have a half cell consisting of the redox couple $Ag^+/Ag$, which for example's sake might be fixed to be at the cathode (i.e. undergoing reduction).
The reaction at the cathode is then
$Ag^+ + e^- \rightarrow Ag$
The standard electrode potential of the $Ag^+/Ag$ couple is $+0.80V$ wrt SHE. I've seen the above reaction written as such:
$Ag^+ + e^- \rightarrow Ag \space\space\space\space\space\space\space\space\space\space\space \mathcal{E} = +0.80V$
I'm confused as to why we write this electrode potential next to the reaction, considering that the electrode potential of a redox couple is reasonably disjoint to the concept of the chemical reaction. Although, at the end of the day, the chemical reaction results in the interfacial potential difference which causes the electrode potential, $\mathcal{E}$ is a property of the electrode, not the chemical reaction.
Is it perhaps just because we want to write the equation of the reaction occurring at a certain electrode *and* the electrode potential of the electrode on the same line?
I'm aware that for associating potentials with written reactions, there exist two different conventions: European, where all reactions are labelled with the reduction potentials of the couple, and American, where oxidation reactions are labelled with the oxidation potentials of the redox couple and likewise reductions with reduction potentials. However, my question is why we need to attach the electrode potential to the chemical reaction in the first place!
That is, ultimately, aren't redox potentials associated with redox couples/electrodes, not reactions? |
What did Richter meant to say with the law of reciprocal proportions and how is it related with an acid base reaction? |
What did Richter mean regarding an acid base reaction? |
I was reading up on LA-ICP-MS and MALDI. All the sources I read for LA-ICP-MS simply say that when the laser hits the sample immediately goes into the gas phase. Why doesn't the laser immediately break fragile molecules?
MALDI makes sense to me. You put the sample in a matrix that absorbs UV really well then hit the matrix-sample mix with a bunch of UV. The matrix explodes essentially, pushing the sample into the gas phase. The key here is that most of the energy of the laser doesn't go into the sample. It goes into the matrix. This is why the sample doesn't break down. LA-ICP-MS doesn't have the matrix to protect the sample so what gives? |
Potential health issues associated with the immediate exposure to toxic propellant gases have been addressed above by Webber GK.
However, a review of the biochemistry literature does suggest that there can also be long-term consequences from radical-induced illness to the lungs (in particular, [see this source](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2626252/), as an example) which may also be a concern here.
As a foundation, I start by looking at the decomposition products likely generated from the discharge of weapons. Starting with gunpowder, per [a source](https://en.wikipedia.org/wiki/Gunpowder):
>Gunpowder...consists of a mixture of sulfur (S), charcoal (C), and potassium nitrate (saltpeter, KNO3). The sulfur and charcoal act as fuels while the saltpeter is an oxidizer.[1][2]
>A simple, commonly cited, chemical equation for the combustion of black powder is:
>$\ce{2 KNO3 + S + 3 C → K2S + N2 + 3 CO2}$
>A balanced, but still simplified, equation is[126]:
>$\ce{10 KNO3 + 3 S + 8 C → 2 K2CO3 + 3 K2SO4 + 6 CO2 + 5 N2}$
I suspect an unmentioned intermediate is sulfite which is converted to sulfate with air contact.
Next, per [Wikipedia on Potassium nitrate]( https://en.wikipedia.org/wiki/Potassium_nitrate), comments on thermal decomposition:
>Between 550–790 °C (1,022–1,454 °F), potassium nitrate reaches a temperature-dependent equilibrium with potassium nitrite:[16]
>$\ce{2 KNO3 ⇌ 2 KNO2 + O2}$
Likely more prevalent, however, is the use of smokeless powder alternatives, which includes nitrocellulose, $\ce{C6H7(NO2)3O5}$ where the more elementary decomposition product could add NH3, NO2 and even some HCN to the list.
Also, the primer employed in bullets is impact-sensitive lead styphnate ($\ce{C6HN3O8Pb}$). As such, I would expect its decomposition to yield CO, CO2, NO, NO2, Pb and water vapor. Also upon the interaction of water and nitrogen dioxide, for example, a possible acid mist:
>$\ce{•NO2 + •NO2 -> N2O4}$
>$\ce{N2O4 + 2 H2O ⇌ HNO2 + HNO3}$
The direct action of $\ce{NO2}$ on $\ce{NH3}$ [may also be possible](https://www.sciencedirect.com/science/article/pii/S0021951708001358) in the presence of $\ce{NO}$ at increasing temperatures.
Interestingly, cited gases $\ce{N2, NO, CO2, SO2, NH3, and O2}$ are colorless. However, the interaction of ammonia and acidic-formed mists could [create a smokescreen](https://books.google.com/books?id=r6V13CyAFvAC&pg=SA7-PA31&lpg=SA7-PA31&dq=ammonia+based+smoke+screen&source=bl&ots=5HFMYA_cBJ&sig=ACfU3U0LKDAe9bTATdLeFpl-Z4orkCOrrQ&hl=en&ppis=_c&sa=X&ved=2ahUKEwi6gMbC9Z3oAhVphOAKHcRhA9sQ6AEwEHoECAoQAQ#v=onepage&q=ammonia%20based%20smoke%20screen&f=false) (in the current discussion, ${NH3}$ with $\ce{H2SO3}$ or $\ce{HNO2}$ or $\ce{HNO3}$ or $\ce{HCN}$…).
To this visible gun smoke, I would add incomplete combustion products including C (as soot) and small amounts of Pb. Also, with the use of KNO3, several potassium salts (sulfide, sulfite, nitrite, sulfate). A largely [confirming source given previously](https://permanent.access.gpo.gov/lps101453/www.bordeninstitute.army.mil/published_volumes/occ_health/OHch10.pdf), to quote:
>This chapter primarily considers the risks of exposure via inhalation, the skin, and the eyes to the major combustion products of commonly used solid propellants—carbon monoxide, ammonia, hydrogen chloride, oxides of nitrogen and sulfur, and lead—in army weapons systems.
However, a rifle’s [barrel does wear down](https://www.thetruthaboutguns.com/how-many-rounds-can-you-shoot-before-a-barrel-loses-accuracty-and-is-worn-out/) due to nozzle pressure and friction generated heat. As such, I would further add trace amounts of iron and chromium metal particles to the outgassing as well, where the presence of transition metals in the lungs could be critical to further reactions.
In particular, with respect to chemistry sourcing radicals (which could produce in time health issues), I start with Josef Prousek’s book "Fenton chemistry in biology and medicine" by, to quote reaction (15) on page 2330, a general depiction of Fenton-type reactions, to quote:
>For Fe(II) and Cu(I), this situation can be generally depicted as follows [20,39],
>$\ce{Fe2+/Cu+ + HOX → Fe3+/Cu2+ + •OH + X-}$ (15)
>where X = Cl, ONO, and SCN.
Assuming HOX could also represent, in the current case with NO2 creation, HONO formation.
Now, a corresponding possible reactions in the current context:
>$\ce{Fe2+/Cr2+ + HONO → Fe3+/Cr3+ + •OH + NO-}$
where $\ce{NO-}$ is more correctly depicted as hyponitrite anion, $\ce{N2O2(2−)}$.
Further, in the human body, the presence of ascorbic acid is known to provide some recycling of ferric (and likely chromium/other transition metal) ions back to ferrous to keep a Fenton-type reaction active (as a reference, see, for example, ['Generation of Hydroxyl Radicals from Dissolved Transition Metals in Surrogate Lung Fluid Solutions'](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2626252/) by Edgar Vidrio, at al.
The cited work by Vidrio notes oxygen and solvated electrons could lead to the creation of the superoxide radical anion, capable of reducing Fe3+ back to Fe2+, thereby promoting cyclic activity in the reaction system:
>$\ce{O2 + e- ⇌ •O2-}$
>$\ce{H+ + •O2- ⇌ •HO2}$
>$\ce{•O2- + Fe3+ ⇌ O2 + Fe2+}$ (a reversible reaction)
>$\ce{Fe2+ + H+ + •HO2 -> Fe3+ + H2O2}$
>$\ce{Fe2+ + H2O2 + H+ -> Fe3+ + •OH + H2O}$
Where the possible creation of the powerful hydroxyl radical is problematic from a health perspective as it can extract a hydrogen atom from any organic (forming water), including DNA, potential leading to health issues.
|
I made a dry cell battery from zinc (Zn), carbon (C) and ammonium chloride (NH4Cl) which produced a current of 0.4 amps and voltage of 1.1V. However when I could not find the redox reaction that was occurring.
What is the chemical reaction happening in the cell? |
We might have a half cell consisting of the redox couple $\ce{Ag+}/\ce{Ag}$, which for example's sake might be fixed to be at the cathode (i.e. undergoing reduction).
The reaction at the cathode is then
$$\ce{Ag+ + e- -> Ag}$$
The standard electrode potential of the $\ce{Ag+}/\ce{Ag}$ couple is $+0.80\ \mathrm V$ with respect to SHE. I've seen the above reaction written as such:
$$\ce{Ag+ + e- <=> Ag} \quad E = +0.80\ \mathrm V$$
I'm confused as to why we write this electrode potential next to the reaction, considering that the electrode potential of a redox couple is reasonably disjoint to the concept of the chemical reaction. Although, at the end of the day, the chemical reaction results in the interfacial potential difference which causes the electrode potential, $E$ is a property of the electrode, not the chemical reaction.
Is it perhaps just because we want to write the equation of the reaction occurring at a certain electrode *and* the electrode potential of the electrode on the same line?
I'm aware that for associating potentials with written reactions, there exist two different conventions: European, where all reactions are labelled with the reduction potentials of the couple, and American, where oxidation reactions are labelled with the oxidation potentials of the redox couple and likewise reductions with reduction potentials. However, my question is why we need to attach the electrode potential to the chemical reaction in the first place!
That is, ultimately, aren't redox potentials associated with redox couples/electrodes, not reactions? |
Why does the ground state of a Li atom have a total spin of S = 1/2? I get that the total z component of the spin has to be either Ms = 1/2 or Ms = -1/2 because of the Pauli exclusion principle, but that could also correspond to a total spin of S = 3/2, so why is it always S = 1/2? |
I have recently got a custom-made ring from a jeweler. It’s made from a byzantine-period bronze ring enveloped in a gold bangle. The bronze ring is “glued” onto the gold ring through some kind of resin, as far as he told me.
Would bimetalism with rhe corrosion of the bronze ring happen?
Thank you!
 |
Will galvanic corrosion happen on a ring made of gold and bronze? |
Does storing apples alongside potatoes keep potatoes from sprouting? |
I'm looking for filter papers to extract silicon nanoparticles after acid etching. I found that much of my material is get wasted with my Whatman Grade 4 filter paper. I am thinking to use membrane filter papers to get the maximum amount of nanoparticles. However, there are hydrophobic and hydrophilic varieties in the market. I'm confused. Also, is it possible to peel off the nanoparticle layer from the membrane surface?
Thank you |
Which is the best kind of filter papers to use to extract silicon nanoparticles after acid wash, hydeophobic or hydrophilic? |
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)
>
>
>
> 1. U.S. Army 1855 - 1 beeswax, 3 tallow.
>
>
>
> 2. U.S. Army 1861 - 8 beeswax, 1 tallow.
>
>
>
> 3. U.S. Army 1873 - 8 bayberry wax, 1 graphite.
>
>
>
> 4. U.S. Army 1880 and thereafter - Japan wax.
>
>
>
> 5. Sharps Rifle Co., 1878 - 1 beeswax, 2 sperm oil.
>
>
>
> 6. Massachusetts Arms Co. (Maynard rifle), 1890 - 1 beeswax, 3 tallow.
>
>
>
> 7. Marlin Firearms Co., 1891 - 1 beeswax, 4 tallow.
>
>
>
> 8. Smith & Wesson, 1891 - tallow.
>
>
>
> 9. 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.
>
>
>
> 10. Automobile door latch stick lubricant, U.S. Patent 1,920,161
>
>
>
> 11. (1931) - 5 paraffin wax, 3 petroleum jelly, 2 oil.
>
>
>
> 12. 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.
>
>
>
> 13. Any mixture containing paraffin wax *must* include a plasticizer, such as petrolatum. Microcrystalline petroleum waxes may be used
> as-is.
>
>
>
> 14. 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? |
Are petroleum-based products prone to produce hard residues with black powder? |
I don't really get the real meaning of the electrochemical stability window. I googled a lot, and the only thing I understand about the electrochemical stability window is that it's the voltage range that the substance is not oxidized and reduced. However, what does this term imply? I mean, I wonder that how we use this concept in practice.
|
What is the hidden meaning of electrochemical stability window? |
Potential health issues associated with the immediate exposure to toxic propellant gases have been addressed above by Webber GK.
However, a review of the biochemistry literature does suggest that there can also be long-term consequences from radical-induced illness to the lungs (in particular, [see this source](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2626252/), as an example) which may also be a concern here.
As a foundation, I start by looking at the decomposition products likely generated from the discharge of weapons. Starting with gunpowder, per [a source](https://en.wikipedia.org/wiki/Gunpowder):
>Gunpowder...consists of a mixture of sulfur (S), charcoal (C), and potassium nitrate (saltpeter, KNO3). The sulfur and charcoal act as fuels while the saltpeter is an oxidizer.[1][2]
>A simple, commonly cited, chemical equation for the combustion of black powder is:
>$\ce{2 KNO3 + S + 3 C → K2S + N2 + 3 CO2}$
>A balanced, but still simplified, equation is[126]:
>$\ce{10 KNO3 + 3 S + 8 C → 2 K2CO3 + 3 K2SO4 + 6 CO2 + 5 N2}$
I suspect an unmentioned intermediate is sulfite which is converted to sulfate with air contact.
Next, per [Wikipedia on Potassium nitrate]( https://en.wikipedia.org/wiki/Potassium_nitrate), comments on thermal decomposition:
>Between 550–790 °C (1,022–1,454 °F), potassium nitrate reaches a temperature-dependent equilibrium with potassium nitrite:[16]
>$\ce{2 KNO3 ⇌ 2 KNO2 + O2}$
Likely more prevalent, however, is the use of smokeless powder alternatives, which includes nitrocellulose, $\ce{C6H7(NO2)3O5}$ where the more elementary decomposition product could add NH3, NO2 and even some HCN to the list.
Also, the primer employed in bullets is impact-sensitive lead styphnate ($\ce{C6HN3O8Pb}$). As such, I would expect its decomposition to yield CO, CO2, NO, NO2, Pb and water vapor. Also upon the interaction of water and nitrogen dioxide, for example, a possible acid mist:
>$\ce{•NO2 + •NO2 -> N2O4}$
>$\ce{N2O4 + 2 H2O ⇌ HNO2 + HNO3}$
The direct action of $\ce{NO2}$ on $\ce{NH3}$ [may also be possible](https://www.sciencedirect.com/science/article/pii/S0021951708001358) in the presence of $\ce{NO}$ at increasing temperatures.
Interestingly, cited gases $\ce{N2, NO, CO2, SO2, NH3, and O2}$ are colorless. However, the interaction of ammonia and acidic-formed mists could [create a smokescreen](https://books.google.com/books?id=r6V13CyAFvAC&pg=SA7-PA31&lpg=SA7-PA31&dq=ammonia+based+smoke+screen&source=bl&ots=5HFMYA_cBJ&sig=ACfU3U0LKDAe9bTATdLeFpl-Z4orkCOrrQ&hl=en&ppis=_c&sa=X&ved=2ahUKEwi6gMbC9Z3oAhVphOAKHcRhA9sQ6AEwEHoECAoQAQ#v=onepage&q=ammonia%20based%20smoke%20screen&f=false) (in the current discussion, ${NH3}$ with $\ce{H2SO3}$ or $\ce{HNO2}$ or $\ce{HNO3}$ or $\ce{HCN}$…).
To this visible gun smoke, I would add incomplete combustion products including C (as soot) and small amounts of Pb. Also, with the use of KNO3, several potassium salts (sulfide, sulfite, nitrite, sulfate). A largely [confirming source given previously](https://permanent.access.gpo.gov/lps101453/www.bordeninstitute.army.mil/published_volumes/occ_health/OHch10.pdf), to quote:
>This chapter primarily considers the risks of exposure via inhalation, the skin, and the eyes to the major combustion products of commonly used solid propellants—carbon monoxide, ammonia, hydrogen chloride, oxides of nitrogen and sulfur, and lead—in army weapons systems.
However, a rifle’s [barrel does wear down](https://www.thetruthaboutguns.com/how-many-rounds-can-you-shoot-before-a-barrel-loses-accuracty-and-is-worn-out/) due to nozzle pressure and friction generated heat. As such, I would further add trace amounts of iron and chromium metal particles to the outgassing as well, where the presence of transition metals in the lungs could be critical to further reactions.
In particular, with respect to chemistry sourcing radicals (which could produce in time health issues), I start with Josef Prousek’s book "Fenton chemistry in biology and medicine" by, to quote reaction (15) on page 2330, a general depiction of Fenton-type reactions, to quote:
>For Fe(II) and Cu(I), this situation can be generally depicted as follows [20,39],
>$\ce{Fe(II)/Cu(I) + HOX → Fe(III)/Cu(II) + •OH + X-}$ (15)
>where X = Cl, ONO, and SCN.
Assuming HOX could also represent, in the current case with NO2 creation, HONO formation.
Now, a corresponding possible reactions in the current context:
>$\ce{Fe(II)/Cr(II) + HONO → Fe(III)/Cr(III) + •OH + NO-}$
where $\ce{NO-}$ is more correctly depicted as hyponitrite anion, $\ce{N2O2(2−)}$.
Further, in the human body, the presence of ascorbic acid is known to provide some recycling of ferric (and likely chromium/other transition metal) ions back to ferrous to keep a Fenton-type reaction active (as a reference, see, for example, ['Generation of Hydroxyl Radicals from Dissolved Transition Metals in Surrogate Lung Fluid Solutions'](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2626252/) by Edgar Vidrio, at al.
The cited work by Vidrio notes oxygen and solvated electrons could lead to the creation of the superoxide radical anion, capable of reducing Fe3+ back to Fe2+, thereby promoting cyclic activity in the reaction system:
>$\ce{O2 + e- ⇌ •O2-}$
>$\ce{H+ + •O2- ⇌ •HO2}$
>$\ce{•O2- + Fe(III) ⇌ O2 + Fe(II)}$ (a reversible reaction)
>$\ce{Fe(II) + H+ + •HO2 -> Fe(III) + H2O2}$
>$\ce{Fe(II) + H2O2 + H+ -> Fe(III) + •OH + H2O}$
Where the possible creation of the powerful hydroxyl radical is problematic from a health perspective as it can extract a hydrogen atom from any organic (forming water), including DNA, potential leading to health issues.
|
The electrochemical stability window is most important when considering components of an electrochemical system that you **do not** want to be oxidized or reduced. This refers most often to the electrolyte or protective coatings.
For example, in lithium ion batteries it is highly desirable that the electrolyte does not react/change/degrade in any way as a result of battery charging/discharging or even in storage. A lithium ion battery typically has a voltage of 3.6 V. The electrolytes used are either lithium salts in organic solvents (ethylene carbonate, etc), solid ceramics, or polymerics electrolytes. If the electrolyte was water based, the electrochemical stability window would only be 1.2 V.
Why 1.2 V?
The standard reduction potential of water is 0.0 V (vs SHE)
The standard oxidation potential of water is 1.2 V (vs SHE)
You can not operate a 3.6 V lithium ion battery with an aqueous electrolyte because the electrolyte itself would react, creating dangerous hydrogen and oxygen gas. So you need an electrolyte with a larger stability window. |
Our college is switching to teaching online mid-semester in hopes of slowing the spread of Covid-19. All the molecular model kits are still on campus. How could you build a model of tetrahedral coordination (say methane) from materials found at home?
I'm aware of computer visualizations (and will make those available), but I think having a physical model when first encountering three-dimensional structures adds value. I made a model from lawn toys (see below), but these are not common household items.
[![enter image description here][1]][1]
[1]: https://i.stack.imgur.com/hWBiy.gif |
How can you build a model of tetrahedral coordination from objects found at home? |
Inflate balloons, and tie them «at their stem» like a bouquet of flowers. If you take four of them, not too much inflated, you well demonstrate a situation close to $sp^3$ hybridization. These models equally work well in larger lecture halls by the way, and _intentionally_ using different colors allows many options.
[![enter image description here][1]][1]
([source][2])
[![enter image description here][3]][3]
([screen photo][4]
You need some worked examples? See videos like [this][5] or [this][4].
You need a scientific paper? Well, there are as well, e.g., [this][6] (open access) expanding the picture to extended $\pi$-systems:
[![enter image description here][7]][7]
[![enter image description here][8]][8]
[1]: https://i.stack.imgur.com/7kLIL.jpg
[2]: https://lecturedemos.chem.umass.edu/molecularStructure.html)
[3]: https://i.stack.imgur.com/5hS83.png
[4]: https://www.youtube.com/watch?v=b0KvfvJi-vk
[5]: https://www.youtube.com/watch?v=unjjYOzEjuY
[6]: http://pubs.sciepub.com/wjce/6/2/5/index.html
[7]: https://i.stack.imgur.com/tke43.png
[8]: https://i.stack.imgur.com/FZ5cc.png |
[An interesting study](http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X2004000600009), to quote:
>In terms of caloric content, ethanol is a unique drug whose oxidation by alcohol dehydrogenase (ADH) produces 7.1 kcal per gram of ethanol oxidized. However, it is not known to what extent these calories are converted into body weight. There is no controversy about the malnutrition produced by chronic ethanol intake in alcoholics. In addition to the known toxic effects on absorption and synthesis of essential nutrients (1), some important metabolic changes occur. Pirola and Lieber (2) reported that activation of the microsomal ethanol oxidizing system (MEOS) in hepatocytes of alcoholics may consume one third of the caloric content of ethanol and impair ATP synthesis. Lands and Zakhari (3) suggested the existence of a futile cycle in ethanol metabolism which would account for a loss of six ATPs per gram of ethanol oxidized. They proposed that ethanol may be oxidized to acetaldehyde, consuming three ATPs, and acetaldehyde may be again reduced to ethanol, consuming three extra ATPs.
However, there is some controversy about what happens to ethanol calories when consumption is moderate and not related to the metabolic changes of the liver that characterize chronic ethanol intake. It has been suggested that calories derived from ethanol may function as do calories derived from carbohydrates, producing a thermogenesis value of about 10% (4,5). This thermogenic value may be higher than that of fatty food (3%) and lower than that of proteins (about 20%) (6).
>The contribution of calories provided by ethanol to body weight gain has also been studied but there seems to be no consensus about the data from animal and human studies.
>Moderate ethanol consumption seems to favor an increase in fat storage and could result in weight gain, especially in overweight individuals (7). In an epidemiological study involving 89,538 women and 48,493 men, Colditz et al. (8) reported a strong negative association between alcohol intake and body weight index for women and the absence of this association for men.
>Animal studies are consistent in reporting a decrease in the body weight of rats receiving ethanol solutions as the only source of liquids. Concentrations of ethanol as low as 5% (v/v), which are similar to the ethanol content of a Brazilian beer, or as high as 40% (v/v), solution similar to spirit drinks, are related to decreased body weight gain (9). Similar results have been reported for 20% (v/v) ethanol solution (10).
>Different results have been obtained for malnourished animals. Da-Silva et al. (11), studying rats which had been treated with ethanol for 90 days, reported a significant weight gain by malnourished rats (50% food restriction) drinking a 20% (v/v) ethanol solution when compared to malnourished rats drinking water. A more recent study (12) reported improvement in somatic and motor development and a decrease in the mortality rate of the offspring of malnourished rats drinking low doses of ethanol (5%, v/v). These data suggest that malnourished rats can benefit from ethanol calories.
>In summary, in spite of the large number of studies on the effects of ethanol in well-nourished animals and humans, there is still controversy about how well ethanol-derived calories can be utilized. Fewer studies are available about special physiological conditions such as malnutrition. Over the last few years, scientific research has mainly focused on obesity, an increasing problem in developed countries, which led us to the false belief that malnutrition was no longer a problem worth investigating. However, there are still 800 million malnourished people in the world (13). The decreasing interest of the scientific community in problems related to malnutrition has left many questions without an answer. Ethanol consumption and its consequences on the malnourished organism are among them.
>In view of the importance of malnutrition in Brazil - 22% of the population or 40 million people are malnourished (14), as well as ethanol consumption and alcoholism - 11% of Brazilian population are alcoholics (15), the aim of the present study was to assess the use of ethanol calories in a dose/effect model by evaluating body weight before and after the installation of malnutrition.
My take, ethanol is apparently somewhat unique and there remains some controversy about how well ethanol-derived calories can be utilized. Study classification factors include well-nourished vs. malnourished, low doses (5%) vs high doses (20%), producing significant variations in effects. |
An [interesting study](http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X2004000600009), 'Can calories from ethanol contribute to body weight preservation by malnourished rats?', to quote:
>In terms of caloric content, ethanol is a unique drug whose oxidation by alcohol dehydrogenase (ADH) produces 7.1 kcal per gram of ethanol oxidized. However, it is not known to what extent these calories are converted into body weight. There is no controversy about the malnutrition produced by chronic ethanol intake in alcoholics. In addition to the known toxic effects on absorption and synthesis of essential nutrients (1), some important metabolic changes occur. Pirola and Lieber (2) reported that activation of the microsomal ethanol oxidizing system (MEOS) in hepatocytes of alcoholics may consume one third of the caloric content of ethanol and impair ATP synthesis. Lands and Zakhari (3) suggested the existence of a futile cycle in ethanol metabolism which would account for a loss of six ATPs per gram of ethanol oxidized. They proposed that ethanol may be oxidized to acetaldehyde, consuming three ATPs, and acetaldehyde may be again reduced to ethanol, consuming three extra ATPs.
However, there is some controversy about what happens to ethanol calories when consumption is moderate and not related to the metabolic changes of the liver that characterize chronic ethanol intake. It has been suggested that calories derived from ethanol may function as do calories derived from carbohydrates, producing a thermogenesis value of about 10% (4,5). This thermogenic value may be higher than that of fatty food (3%) and lower than that of proteins (about 20%) (6).
>The contribution of calories provided by ethanol to body weight gain has also been studied but there seems to be no consensus about the data from animal and human studies.
>Moderate ethanol consumption seems to favor an increase in fat storage and could result in weight gain, especially in overweight individuals (7). In an epidemiological study involving 89,538 women and 48,493 men, Colditz et al. (8) reported a strong negative association between alcohol intake and body weight index for women and the absence of this association for men.
>Animal studies are consistent in reporting a decrease in the body weight of rats receiving ethanol solutions as the only source of liquids. Concentrations of ethanol as low as 5% (v/v), which are similar to the ethanol content of a Brazilian beer, or as high as 40% (v/v), solution similar to spirit drinks, are related to decreased body weight gain (9). Similar results have been reported for 20% (v/v) ethanol solution (10).
>Different results have been obtained for malnourished animals. Da-Silva et al. (11), studying rats which had been treated with ethanol for 90 days, reported a significant weight gain by malnourished rats (50% food restriction) drinking a 20% (v/v) ethanol solution when compared to malnourished rats drinking water. A more recent study (12) reported improvement in somatic and motor development and a decrease in the mortality rate of the offspring of malnourished rats drinking low doses of ethanol (5%, v/v). These data suggest that malnourished rats can benefit from ethanol calories.
>In summary, in spite of the large number of studies on the effects of ethanol in well-nourished animals and humans, there is still controversy about how well ethanol-derived calories can be utilized. Fewer studies are available about special physiological conditions such as malnutrition. Over the last few years, scientific research has mainly focused on obesity, an increasing problem in developed countries, which led us to the false belief that malnutrition was no longer a problem worth investigating. However, there are still 800 million malnourished people in the world (13). The decreasing interest of the scientific community in problems related to malnutrition has left many questions without an answer. Ethanol consumption and its consequences on the malnourished organism are among them.
>In view of the importance of malnutrition in Brazil - 22% of the population or 40 million people are malnourished (14), as well as ethanol consumption and alcoholism - 11% of Brazilian population are alcoholics (15), the aim of the present study was to assess the use of ethanol calories in a dose/effect model by evaluating body weight before and after the installation of malnutrition.
My take, ethanol is apparently somewhat unique and there remains some controversy about how well ethanol-derived calories can be utilized. Study classification factors include well-nourished vs. malnourished, low doses (5%) vs high doses (20%), producing significant variations in effects. |
I’m wondering what would happen if the filter paper in a vacuum filtration process is bigger than the buchner funnel diameter?
I mean would some differences occurs? Or would the whole experiment damage? If yes, may I know how and why?
|
What happens if the filter paper in vacuum filtration is BIGGER than the buchner funnel diameter? |
Here is a rather simple structure explanation presented on [this site](https://www.masterorganicchemistry.com/2010/07/09/chemical-tetris/). To quote, where 'pieces' refer to an organic molecular with a non-symmetric branching structure:
>You’ll notice something – the simpler the pieces are, the easier they are to stack together, which provides a tighter fit with fewer spaces. Here, by putting a kink in the block, we make them harder to stack.
>What’s this got to do with chemistry?
>When compounds freeze, the process is a lot like stacking bricks. The more symmetrical the molecules are, the easier it will be and the fewer spaces there will be between the molecules. Fewer spaces = better stacking. Hence, when you compare hexane to its structural isomer, 2-methylpentane, hexane has a much higher melting point due to the regular arrangement of its structure.
>Better stacking, higher melting point. Case closed. Right? Not quite.
>It’s also about surface area.
>It looks like as we increase branching, we’re increasing melting point and decreasing boiling point. What’s going on?
>Going from “branched” to “highly branched” makes a molecule more compact and sphere-like. As the surface area of the molecule decreases (remember that spheres have the lowest surface area/volume ratio of any shape) they will become more compact and thus easier to pack. This explains the melting point phenomenon.
>Boiling point is related to the forces between molecules, which in the case of hydrocarbons is Van Der Waals interactions. If you’ve ever seen microscope images of a gecko’s feet – which allow it to climb walls – you’ll see that there is no adhesive but the pads contain a tremendous amount of surface area. It’s all about the Van der Waals interactions.
>As we decrease surface area, we are going to decrease intermolecular Van Der Waals interaction and therefore decrease boiling point.
The summary relationships are presented as follows:
>linear versus branched —> higher melting/boiling points due to better stacking and surface area contact.
>highly branched vs. branched —> more sphere-like –> better stacking –> higher melting point
>highly branched vs. branched —>more sphere-like – -> lower surface area —> lower boiling point.
The above connects boiling point to branching structure, and this paper "Hypothetical Thermodynamic Properties: The Boiling and Critical Temperatures of Polyethylene and Polytetrafluoroethylene" [found here](http://umsl.edu/~chickosj/JSCPUBS/bp.pdf) links BP to thermodynamics. Per the opening reference statement: "A lower heat of formation is equivalent to a higher thermodynamic stability".
This completes the argument as to why the heat of formation decreases for organic radicals with decreased size and degrees of branching. |
Here is a rather simple structure explanation presented on [this site](https://www.masterorganicchemistry.com/2010/07/09/chemical-tetris/). To quote, where 'pieces' refer to an organic molecular with a non-symmetric branching structure:
>You’ll notice something – the simpler the pieces are, the easier they are to stack together, which provides a tighter fit with fewer spaces. Here, by putting a kink in the block, we make them harder to stack.
>What’s this got to do with chemistry?
>When compounds freeze, the process is a lot like stacking bricks. The more symmetrical the molecules are, the easier it will be and the fewer spaces there will be between the molecules. Fewer spaces = better stacking. Hence, when you compare hexane to its structural isomer, 2-methylpentane, hexane has a much higher melting point due to the regular arrangement of its structure.
>Better stacking, higher melting point. Case closed. Right? Not quite.
>It’s also about surface area [...]
>It looks like as we increase branching, we’re increasing melting point and decreasing boiling point. What’s going on? [...]
>Going from “branched” to “highly branched” makes a molecule more compact and sphere-like. As the surface area of the molecule decreases (remember that spheres have the lowest surface area/volume ratio of any shape) they will become more compact and thus easier to pack. This explains the melting point phenomenon [...]
>Boiling point is related to the forces between molecules, which in the case of hydrocarbons is Van Der Waals interactions. If you’ve ever seen microscope images of a gecko’s feet – which allow it to climb walls – you’ll see that there is no adhesive but the pads contain a tremendous amount of surface area. It’s all about the Van der Waals interactions.
>As we decrease surface area, we are going to decrease intermolecular Van Der Waals interaction and therefore decrease boiling point.
The summary relationships are presented as follows:
>linear versus branched —> higher melting/boiling points due to better stacking and surface area contact.
>highly branched vs. branched —> more sphere-like –> better stacking –> higher melting point
>highly branched vs. branched —>more sphere-like – -> lower surface area —> lower boiling point.
The above connects boiling point to branching structure, and this paper "Hypothetical Thermodynamic Properties: The Boiling and Critical Temperatures of Polyethylene and Polytetrafluoroethylene" [found here](http://umsl.edu/~chickosj/JSCPUBS/bp.pdf) links BP to thermodynamics. Per the opening reference statement: "A lower heat of formation is equivalent to a higher thermodynamic stability".
This completes the argument as to why the heat of formation decreases for organic radicals with decreased size and degrees of branching. |
According to my textbook,
> Lattice enthalpy is the enthalpy change that occurs when one mole of a solid ionic compound is separated into gaseous ions under standard conditions.$^1$
According to the same textbook, this is an endothermic process, which makes sense as a lattice is generally held together by strong ionic bonds and thus would require energy to separate the atoms. The following diagram is given for the born-haber cycle in the textbook:
[![enter image description here][1]][1]
The diagram supports the definition as the enthalpy of the individual gaseous atoms is greater than that of the lattice, i.e. the arrow moves up. **However**, as I was working through past papers by the International Baccalaureate, a question asked to draw the born-haber cycle for LiF.$^2$ This was the answer:
[![enter image description here][2]][2]
In this case, the arrow is pointing down for the lattice enthalpy. To me, this does not suite the definition of lattice enthalpy as separating a lattice into its ions would require energy and not release energy. Hence, should the arrow not be pointing upwards for $\ce{LiF_{(s)}}$ to $\ce{Li^+_{(g)} + Cl^-_{(g)}}$? Am I making a fundamental error, is the case for NaCl different to LiF or is the answer wrong?
Works Cited:
1. Pearson Baccalaureate: Higher Level Chemistry 2nd Edition. By Catrin Brown and Mike Ford
2. International Baccalaureate
[1]: https://i.stack.imgur.com/ZcL2e.png
[2]: https://i.stack.imgur.com/f5r8Q.png |
I need to determine as many J values as I can for 3-methoxybenzaldehyde. The peaks overlap a lot, and I don't see the expected ddd or dt pattern that I would expect for the hydrogen on carbon 6. The HSQC I was given has the clearest peaks for the H NMR, so I attached that. Maybe someone with more NMR experience can help me tease apart the signals?
[![enter image description here][1]][1]
[1]: https://i.stack.imgur.com/FfrbI.png |
NOTE: Please do not delete this question. It is not a personal health question. **The question has broad utility, in cases where others find themselves in social-distancing or quarantine with need for surface sanitizer, and their only available ingredients are water and powdered oxy-bleach.**
I need a quantity of surface sanitizer to decontaminate boxes delivered to the house during the Coronavirus19 social-distancing period.
CDC and WHO say 0.5% hydrogen peroxide solution will destroy coronavirus19. And powdered oxy-bleach a.k.a. Sodium percarbonate contains 32.5% by weight of hydrogen peroxide, I'll call it roughly a third.
So to make a water solution of hydrogen peroxide using powdered oxy-bleach, I'm thinking I need to add enough powdered oxy-bleach (by weight) to equal 3 x 0.5% of the weight of the water. I.e, for a gallon of solution, 1.5% of 8.3 pounds, thus 0.12 lb, or ~2 oz.
A friend checked this and agreed, saying:
"A 0.5% H2O2 solution in water will consist of (per gallon): 0.42 lbs of H2O2 and 7.9 lbs of H2O. To get 0.42 lbs of H2O2 out of Oxy-bleach (32.5% H2O2), divide 0.42 by 0.325, which = 0.128 lbs or 2.0529230769 ounces..."
Can anyone poke holes in our thinking? Or refine it? **Or suggest ways to make it easier for the lay-person locked-in without access to other surface sanitizers?**
Thank you in advance! |
I'm taking an undergraduate level class on computer based drug design. The class is more for biology students than people with a strong understanding in physics and computer science.
With that said, I'm having trouble discerning the difference between what molecular docking and scoring functions are.
To me they seem like they are the same thing since they have the same goal, which is to figure out which ligands have the strongest binding affinity to a target protein. But what are the different ways each method accomplishes that and when would each method be used if (to me) each method does the same thing? Is a scoring function a way to check the validity of a docking simulation, if so how? |
Difference between docking and scoring? |
I am completely new to using OpenBabel software.
I have about 9000 pdb files to which, I want to add hydrogens. It will be a very hectic task to open all of them 1 by 1 and then convert each of them. Is there any way I could convert all of them simultaneously.
Also, can you please tell me how to correctly select the output file? It asks for a destination file to which, it appends/overwrites the output. Is there a way I could choose the destination where it would create another .pdb file and save the output in it? I guess I am missing something here while choosing the output file.
Thanks in advance. Also, I asked a similar question before which was closed. Considering I am new with OpenBabel, if any further information is required or if there is some issue, please tell me so that I may improve my question.
[![This is a screenshot for reference][1]][1]
[1]: https://i.stack.imgur.com/Ll8TD.png |
Is NH3 a strong ligand or weak? |
If a synthesis reaction is a reaction that two or more substances react together to form just one product. Then how is it that photosynthesis has two products and the end of the which are glucose and oxygen? |
Yes, do use household dilute H2O2 but, in general, do not use commercial percarbonates powders as there contains an additive to convert the friendly percarbonate into more powerful Peracetic acid (PAA). The latter allows the otherwise weak bleaching power of the H2O2 to compete with chlorine-based bleaching. However, this comes at a price (safety). Hence, the dire warning labels, usually in at least two languages, on Oxi-Bleach and generic related products.
I quote myself on this subject:
>Sodium percarbonate is chemically just an addition compound of Na2CO3 and Hydrogen peroxide.
>Also, while Sodium carbonate and Sodium percarbonate (basically Na2CO3 and 3Na2CO3.2H2O2) are often listed as the main ingredients in typical chlorine free bleach, an additive, TAED, which acts as a key activator ([see, for example]( https://en.m.wikipedia.org/wiki/OxiClean)) is not even listed on the label. TetraAcetylEthyleneDiamine is apparently commonly employed as a bleach activator in many laundry products ([see this](https://en.m.wikipedia.org/wiki/Tetraacetylethylenediamine )). TAED reacts with H2O2 in alkaline conditions (referred to as perhydrolysis) creating, in part, Peracetic Acid. The latter PAA is actually preferred over sluggish H2O2 for bleaching. In other words, it is not the H2O2 as the active bleaching agent, but PAA created in situ. So, other than possibly misleading implying that eco friendly hydrogen peroxide is the active agent, it is, in reality, PAA, a probematic compound with associated health concerns (see Marquand, E. C.; et al. , 2007. "Asthma Caused by Peracetic Acid-Hydrogen Peroxide Mixture". J. Occup. Health. 49 (2): 155–158.). Here is a MSDS on an actual PAA mix ( 76-61% water, PAA 20-35%, 3% Acetic acid and 1% H2O2) [available at](https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.peraceticacidsystems.com/downloads/msds.pdf&ved=0ahUKEwiFiJ_e4brTAhUBTSYKHWNSDK8QFggcMAE&usg=AFQjCNHQDWuC2ZCKmHPR4hvSdl3eJTVI2w&sig2=J4EcGfXW-06p54ggP_Q9TQ) which is far from friendly but does eventually totally decompose into harmless O2, CO2, H2O,...
>As such anyone using a commercial percarbonate product should at least be aware of safety issues and that one is likely employing a Peracetic acid mix. |
Yes, do use household dilute H2O2 but, in general, do not use commercial percarbonates powders as there contains an additive to convert the friendly percarbonate into more powerful Peracetic acid (PAA). The latter allows the otherwise weak bleaching power of the H2O2 to compete with chlorine-based bleaching. However, this comes at a price (safety). Hence, the dire warning labels, usually in at least two languages, on Oxi-Bleach and generic related products.
I quote myself on this subject:
>Sodium percarbonate is chemically just an addition compound of Na2CO3 and Hydrogen peroxide.
>Also, while Sodium carbonate and Sodium percarbonate (basically Na2CO3 and 3Na2CO3.2H2O2) are often listed as the main ingredients in typical chlorine free bleach, an additive, TAED, which acts as a key activator ([see, for example]( https://en.m.wikipedia.org/wiki/OxiClean)) is not even listed on the label. TetraAcetylEthyleneDiamine is apparently commonly employed as a bleach activator in many laundry products ([see this](https://en.m.wikipedia.org/wiki/Tetraacetylethylenediamine )). TAED reacts with H2O2 in alkaline conditions (referred to as perhydrolysis) creating, in part, Peracetic Acid. The latter PAA is actually preferred over sluggish H2O2 for bleaching. In other words, it is not the H2O2 as the active bleaching agent, but PAA created in situ. So, other than possibly misleading implying that eco friendly hydrogen peroxide is the active agent, it is, in reality, PAA, a probematic compound with associated health concerns (see Marquand, E. C.; et al. , 2007. "Asthma Caused by Peracetic Acid-Hydrogen Peroxide Mixture". J. Occup. Health. 49 (2): 155–158.). Here is a MSDS on an actual PAA mix ( 76-61% water, PAA 20-35%, 3% Acetic acid and 1% H2O2) [available at](https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.peraceticacidsystems.com/downloads/msds.pdf&ved=0ahUKEwiFiJ_e4brTAhUBTSYKHWNSDK8QFggcMAE&usg=AFQjCNHQDWuC2ZCKmHPR4hvSdl3eJTVI2w&sig2=J4EcGfXW-06p54ggP_Q9TQ) which is far from friendly but does eventually totally decompose into harmless O2, CO2, H2O,...
>As such anyone using a commercial percarbonate product should at least be aware of safety issues and that one is likely employing a Peracetic acid mix.
However, such more powerful PAA based mixtures do have their use and is recommended by the U.S. Military for chemical/biological warfare decontamination protocol (see ["Development of Bicarbonate-Activated Peroxide as a Chemical and Biological Warfare Agent Decontaminant"](https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.dtic.mil/dtic/tr/fulltext/u2/a455611.pdf&ved=0ahUKEwi8yM-QrLPXAhVFeCYKHWMKDSkQFgg9MAM&usg=AOvVaw0DyOiHVg-2Rh2AnPEJri3b)). So, it is up to the user to weigh the relative risk of the situation.
|
When I was kid and got a huge cut on my finger, I remember my grandmother putting lots of kerosene on my wound, as there was no health facility around.
I want to confirm. Do chemists agree on the antiseptic role of kerosene, or was grandma just using useless remedy? |
Electron transfer rates (k) as derived from Marcus theory assumes i) thermal equilibrium and ii) neglects quantum nature of low-frequency phonon modes. Can anyone explain what is at the heart of these two assumptions? Thanks a lot!
I read this in the context of the electron transfer process in organic semiconductors. |
If a synthesis reaction is a reaction in which two or more substances react together to form just one product, then how is it that photosynthesis has two products; glucose and oxygen? |
I think you're being a little too strict with your definition of what a synthesis reaction is. A better way to describe it might be building more complex molecules from simpler ones.
Wouldn't you say C6H12O6 is more complex than CO2 and H2O? |
Here are two common ways of measuring the entropy change in a reaction:
1. Measure the equilibrium constant $K$ at multiple temperatures. This gives you the Gibbs energy (via $\Delta_r G^\circ = - R T \ln{K}$) and, via the van't Hoff relationship, the enthalpy. You can calculate the entropy from those two.
2. Use microcalorimetry in a titrating mode. You get the enthalpy directly, and the equilibrium constant by fitting the trace (which tells you the extent of reaction at different concentrations). From those two, you obtain the entropy.
The entropy change is concentration-dependent, so once you have the standard entropy of reaction, you might have to correct for concentrations that are different from those at standard state.
> 2) What is the best way to teach entropy (at an introductory level)?
It depends. However, my favorite analogy to use when guessing which state has higher energy is "freedom of atoms to move". This works for solid vs. gas, for bound vs. in solution, and for constrained conformations vs. rotatable bonds. It also hand-wavingly makes the connection to the number of microstates that Martin references in a comment. The other term you sometimes find is "dispersion of energy", which nicely explains how entropy increases when a rock (that fell off a cliff) hits the ground. |
Yes, do use household dilute H2O2 but, in general, do not use commercial percarbonates powders as there contains an additive to convert the friendly percarbonate into more powerful Peracetic acid (PAA). The latter allows the otherwise weak bleaching power of the H2O2 to compete with chlorine-based bleaching. However, this comes at a price (safety). Hence, the dire warning labels, usually in at least two languages, on Oxi-Bleach and generic related products.
I quote myself on this subject:
>Sodium percarbonate is chemically just an addition compound of Na2CO3 and Hydrogen peroxide.
>Also, while Sodium carbonate and Sodium percarbonate (basically Na2CO3 and 3Na2CO3.2H2O2) are often listed as the main ingredients in typical chlorine free bleach, an additive, TAED, which acts as a key activator ([see, for example]( https://en.m.wikipedia.org/wiki/OxiClean)) is not even listed on the label. TetraAcetylEthyleneDiamine is apparently commonly employed as a bleach activator in many laundry products ([see this](https://en.m.wikipedia.org/wiki/Tetraacetylethylenediamine )). TAED reacts with H2O2 in alkaline conditions (referred to as perhydrolysis) creating, in part, Peracetic Acid. The latter PAA is actually preferred over sluggish H2O2 for bleaching. In other words, it is not the H2O2 as the active bleaching agent, but PAA created in situ. So, other than possibly misleading implying that eco friendly hydrogen peroxide is the active agent, it is, in reality, PAA, a probematic compound with associated health concerns (see Marquand, E. C.; et al. , 2007. "Asthma Caused by Peracetic Acid-Hydrogen Peroxide Mixture". J. Occup. Health. 49 (2): 155–158.). Here is a MSDS on an actual PAA mix ( 76-61% water, PAA 20-35%, 3% Acetic acid and 1% H2O2) [available at](https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.peraceticacidsystems.com/downloads/msds.pdf&ved=0ahUKEwiFiJ_e4brTAhUBTSYKHWNSDK8QFggcMAE&usg=AFQjCNHQDWuC2ZCKmHPR4hvSdl3eJTVI2w&sig2=J4EcGfXW-06p54ggP_Q9TQ) which is far from friendly but does eventually totally decompose into harmless O2, CO2, H2O,...
>As such anyone using a commercial percarbonate product should at least be aware of safety issues and that one is likely employing a Peracetic acid mix.
However, such more powerful PAA based mixtures do have their use and is recommended by the U.S. Military as a chemical/biological warfare decontamination protocol (see ["Development of Bicarbonate-Activated Peroxide as a Chemical and Biological Warfare Agent Decontaminant"](https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.dtic.mil/dtic/tr/fulltext/u2/a455611.pdf&ved=0ahUKEwi8yM-QrLPXAhVFeCYKHWMKDSkQFgg9MAM&usg=AOvVaw0DyOiHVg-2Rh2AnPEJri3b)). So, it is up to the user to weigh the relative risks of the situation.
|
In thermodynamics, the heat that transferred to an ideal gas is considered as work that was done on the system? |
My understanding is that a redox couple is an unordered pair of two conjugate species. So we could speak of the redox couple consisting of $Ag$ and $Ag^+$; depending on whether a given redox couple is undergoing oxidation or reduction, we could then write a half equation involving the species given in the redox couple.
In my textbook, it is given as a convention that all redox couples are expressed in the form Ox/Red. So for instance, it states "at anode containing the $Zn^{2+}/Zn$ redox couple, the oxidation half equation is $Zn \rightarrow Zn^{2+} + 2e^-$". This convention makes sense to me, since it doesn't seem that the couple itself refers to a half equation in a given direction. The order of the *half cell* line representation, however, **does** change the order to $Zn | Zn^{2+}$.
However, some texts reverse the order of the written redox couple, which I would interpret as either them writing the couple in the order of the current half equation (which seems wrong) **or** that they are ignoring the order because it is unimportant.
So I wondered whether anyone could clarify, is a redox couple just a pair of species which exist at a given half cell, or do we need to change the order of the written couple depending on the reaction occurring at that half cell? |
Does the order of a written redox couple matter? |
In my QM class we are finding the wave functions of the hydrogen atom. In spherical coordinates, these wave functions are functions of 3 variables: $r,$ $\theta,$ and $\phi.$ My professor stated that "*the wave functions of the electron are called orbitals*".
Say, we are interested in the $l = 0$ (or s-orbitals). Since $l = 0,$ $m = 0.$
$$\psi_{n00}(r,\theta,\phi) = R_{n0}(r)Y_{00}(\theta,\phi) = \left(\frac{1}{4\pi}\right)^{1/2}R_{n0}(r)$$
So, we can set a specific $n$ value. Say, $n = 1,$ and we get the the corresponding 1s orbital. Since we set an $n$ value, the wave function reduces to a function of the radius $r.$ During the lecture, he said that this image:
[![isosurface of the wave function at a constant radius][1]][1]
is an isosurface (or level surface) of the wave function at a constant radius.
I interpreted that as finding the isosurface of a 4D graph, our wave function, at some radius. This isosurface is the the sphere in 3D. What confused me was when he stated that the graph was an "*isosurface of the full orbital*".
What does he mean by the "*full orbital*"? Is this "*full orbital*" something in 4D space?
[1]: https://i.stack.imgur.com/nbTul.png |
I think you're being a little too strict with your definition of what a synthesis reaction is. A better way to describe it might be building more complex molecules from simpler ones.
Wouldn't you say $\ce{C6H12O6}$ is more complex than $\ce{CO2}$ and $\ce{H2O}$? |
>1.
The density at $20^\circ\mathrm{C}$ of a $\pu{0.500 M}$ solution of acetic acid in water is $\pu{1.0042 g/mL}$. What is the molality of the solution? The molar mass of acetic acid is $M(\ce{CH3CO2H})=\pu{60.05 g/mol}$.
>2.
The density at $20^\circ\mathrm{C}$ of a $\pu{0.258 M}$ solution of glucose in water is
$\pu{1.0173 g/mL}$, and the molar mass of glucose is $M(\ce{Glc}) = \pu{180.2 g/mol}$. What is the molarity of the solution?
In question one we can assume a 1 liter solution and in question two we can assume a 100 gram sample. I understand these assumptions are needed to find other information, but when are we justified in making these assumptions? |
In thermodynamics, why is the heat that is transferred to an ideal gas considered as work that was done on the system for an isothermal process? |
I am an oil well integrity engineer. Need help in understanding gas solubility in oil-based drilling mud (OBM) when the mud is gelled. Normally, oil based mud is an emulsion, where continuous phase is some type of oil (~70%), and remaining is dispersed water/brine droplets, various additives to get to desired drilling mud properties. Gas is highly soluble in OBM, mostly due to base oil is it's main component. However, drilling mud is thixotropic and becomes like a gel when static. Don't know exact mechanism, but something like molecules connect to create long chain polymers, thus forming gel (?).
I am trying to understand, if gas is diffused into the mud after it has become like gel, would the gas dissolve in the same way as it would in thin mud (before it's gelled). Considering, how non-polar molecules dissolve in non-polar solvents, I tend to think that not as much gas would dissolve, but I might be wrong. Please, help me. |
Normally protein coordinates are generated from electron density, such as that from X-ray scattering experiment. In my case, I want the reverse - PDB to electron density mesh. I thought it was more trivial and a program should be available. But Google did not give me any luck.
Is there any existing python library/program which converts protein coordinate (pdb) into electron density mesh (custom resolution)? If not, how should one proceed? The orbital and atomistic electron density varies among atom types.
Your suggestion appreciated. |
In my book it is given that first electron gain enthalpy is greater than second for elements. Should we compare the magnitudes in such cases or the actual numbers with signs? Does the same comparision hold with Electron Affinity at 0K? |
For the more recent structures, you can view the density (based on measured diffraction data and the model, so-called 2Fo-Fc density) directly in the protein data bank, e.g. http://www.rcsb.org/3d-view/6QU9?preset=electronDensityMaps:
[![enter image description here][1]][1]
For a theoretical model or a model without deposited diffraction data, you would first have to generate structure factors, and then calculate the electron density. In the simplest case, the electron density would just reflect the density of isolated atoms (i.e. no deformation density). Program suites such as CCP4 (originally in Fortran) or Phenix (in python) are available to do these steps.
In these calculations, the electron density of individual atoms is encoded in so-called atomic form factors (see e.g. http://lampx.tugraz.at/~hadley/ss1/crystaldiffraction/atomicformfactors/formfactors.php), which are fourier transform coefficients of the model electron density for each atom.
[1]: https://i.stack.imgur.com/d9Gka.jpg |
The answer is $AuCl_3 + NaCN$
Now I understand that for electroplating, we need gold to be deposited on the copper article, and the electrolyte must enable that deposition. But I don’t know what is the use of $NaCN$ in the process.
Also, if copper is the cathode, then pure gold should be the anode. But the oxidation potential of gold is very low, then how does it get dissolved in the solution.
Can I get an explanation on this process would work? |
What is the electrolytic bath used in gold-plating of copper articles? |
N2+3H2 ---------> 2NH3, DeltaH = -92.2kj
Now I understand why this reaction isn't carried out in the lowest possible temperature (even though it seems that it should be as it favors the right side of the reaction). As the rate of reaction would be very slow, the amount of NH3 produced would be lesser than the amount that would've been produced if the reaction was carried out at the optimum temperature in a given time span.
Now my question is, why isn't then the reaction carried out at the highest possible temperature since the rate of reaction would be very high and the yield would be very high consequently as well? |
I understand why the reaction
$$\ce{N2 + 3 H2 -> 2 NH3} \qquad \Delta H = \pu{-92.2 kJ mol-1}$$
isn't carried out in the lowest possible temperature (even though it seems that it should be as it favors the right side of the reaction). As the rate of reaction would be very slow, the amount of $\ce{NH3}$ produced would be lesser than the amount that would've been produced if the reaction was carried out at the optimum temperature in a given time span.
Why isn't then the reaction carried out at the highest possible temperature since the rate of reaction would be very high and the yield would be very high consequently as well? |
> What is so acidic...and basic...?
Nothing.
This derives from the historical perception that silica in geological systems and in melts was in the form of silicic acid ($\ce{H2SiO4}$) and the alkali and alkali earth elements were considered as bases.
We now know that in high temperature silicate liquids (that eventually solidifies into slag, or rocks, or glass) there is no acid–base chemistry, at least in the form that we know it from low-temperature aqueous acid–base chemistry. However, the usage of the terms acid and base in relation to rocks and slags still persists, primarily with older professors (who still teach) or in certain parts of the world, such as Russia. Nowadays geologists usually prefer the term "felsic" over the term "acidic" for silica-rich rocks.
Nonetheless, the measure of $\ce{CaO}$ and $\ce{SiO2}$ contents in slags, glasses and rocks is still useful for various reasons. Therefore, the ratio is still calculated and used, and the old name persists. A slightly better parameter, called [optical basicity][1], takes into account the compositional variability other than $\ce{CaO}$ and $\ce{SiO2}$, by adding other oxides such as $\ce{Na2O}$ and $\ce{K2O}$ into the calculation. It is widely used and has many applications.
[1]: https://doi.org/10.1021/ed073p1138 |
Suppose there is a water solution at $25^0C$ with $Na^+$, $Mg^{2+}$ cations and $Cl^-$, $HCO_3^-$ anions. Concentrations of [$Na^+$], [$Mg^{2+}$], [$Cl^-$] and [$HCO_3^-$] are known.
I cannot understand how to apply the **Kohlrausch's law of the independent migration of ions** here: $$ \Lambda_m^0 = \nu_+\lambda_+ + \nu_-\lambda_-$$
How this formula will transform for the solution with many kinds of ions? |
This is the mass spectrum for 4-methylpentan-1-ol
[![enter image description here][1]][1]
From its structural formula, what could be the fragmentation which results in a peak at m/z = 56?
[1]: https://i.stack.imgur.com/XUDbx.png
I was considering a few possibilities; could it be C3H4O+ ? |
Cause of m/z = 56 peak in 4-methyl-1-pentanol? |
Suppose there is a water solution at $\pu{25 °C}$ with $\ce{Na+},$ $\ce{Mg^2+}$ cations and $\ce{Cl-},$ $\ce{HCO3-}$ anions. Concentrations $[\ce{Na+}],$ $[\ce{Mg^2+}],$ $[\ce{Cl^-}]$ and $[\ce{HCO3-}]$ are known.
I cannot understand how to apply the Kohlrausch's law of the independent migration of ions here:
$$\Lambda_\mathrm{m}^0 = \nu_+\lambda_+ + \nu_-\lambda_-$$
How this formula will transform for the solution with many kinds of ions? |
This is the mass spectrum for 4-methylpentan-1-ol:
[![mass spectrum for 4-methylpentan-1-ol][1]][1]
From its structural formula, what could be the fragmentation which results in a peak at $m/z = 56?$
I was considering a few possibilities; could it be $\ce{C3H4O+}?$
[1]: https://i.stack.imgur.com/XUDbx.png |
Suppose there is a water solution at $\pu{25 °C}$ with $\ce{Na+},$ $\ce{Mg^2+}$ cations and $\ce{Cl-},$ $\ce{HCO3-}$ anions. Concentrations $[\ce{Na+}],$ $[\ce{Mg^2+}],$ $[\ce{Cl^-}]$ and $[\ce{HCO3-}]$ are known.
I cannot understand how to apply the Kohlrausch's law of the independent migration of ions here:
$$\Lambda_\mathrm{m}^0 = \nu_+\lambda_+ + \nu_-\lambda_-$$
How this formula will transform for the solution with many kinds of ions?
Edit:
Electroneutrality condition holds, so:
$$[\ce{Na+}]+2 \cdot [\ce{Mg^2+}]=[\ce{Cl^-}]+[\ce{HCO3-}]$$
I've found the table with the limiting ionic conductivities $\lambda$ of each individual ion in water at $\pu{25 °C}$:
$\lambda_{\ce{Na+}} = \pu{50 \cdot 10^{-4} S m2 mol-1}$
$\lambda_{\ce{Mg^2+}} = \pu{106 \cdot 10^{-4} S m2 mol-1}$
$\lambda_{\ce{Cl-}} = \pu{76 \cdot 10^{-4} S m2 mol-1}$
$\lambda_{\ce{HCO3-}} = \pu{45 \cdot 10^{-4} S m2 mol-1}$
But I don't know what values for $\nu$ I should take. |
>A compound $\ce X$ of formula $\ce{C2H5NO2}$ on treatment with $\ce {HNO2}$
$(\ce{NaNO2}+\ce{HCl})$ gives off an inactive gas $\ce Y$ and forms $\ce Z$. When heated with soda lime, $\ce X$ gives $\ce{A(CH5N)}$ soluble in acid. Find the true statements :
>
> 1. $\ce A$ answers carbylamine test.
> 2. $\ce X$ is an amino acid.
> 3. $\ce Y$ is $\ce{CO2}$.
> 4. $\ce Z$ is a hydroxyl acid.
**My attempt :**
$\ce X$ is glycine.
$\ce A$ is methyl amine.
$\ce Y$ is dintrogen.
$\ce Z$ is 2-hydroxy ethanoic acid.
Hence, correct options should be : $1,2,4$. But the answer given is $2,4$.
Can anyone help me to understand if and where I went wrong?
|
>A compound $\ce X$ of formula $\ce{C2H5NO2}$ on treatment with $\ce {HNO2}$
$(\ce{NaNO2}+\ce{HCl})$ gives off an inactive gas $\ce Y$ and forms $\ce Z$. When heated with soda lime, $\ce X$ gives $\ce{A(CH5N)}$ soluble in acid. Find the true statements :
>
> 1. $\ce A$ answers carbylamine test.
> 2. $\ce X$ is an amino acid.
> 3. $\ce Y$ is $\ce{CO2}$.
> 4. $\ce Z$ is a hydroxyl acid.
**My attempt :**
$\ce X$ is glycine.
$\ce A$ is methyl amine.
$\ce Y$ is dinitrogen.
$\ce Z$ is 2-hydroxy ethanoic acid.
Hence, correct options should be : $1,2,4$. But the answer given is $2,4$.
Can anyone help me to understand if and where I went wrong?
|
Why is Electrochemistry often the method of choice for determining Ksp values? |
I need to create a $100\textrm{mL}$ buffer of $\textrm{pH = 9.20}$ with ammonia and ammonium chloride such that $\textrm{pH = }9.20\pm0.50$ with $20\textrm{mL}$ of $0.2\textrm{M } \ce{NaOH}/\ce{HCl}$. I am provided with $0.1\textrm{M}$ ammonia and ammonium chloride.
I used the Henderson-Hasselbalch equation to figure out the relative amounts of $\ce{NH3}$ and $\ce{NH4+}$ I need:
$$
\textrm{pH} = \textrm{pKa} + \log \frac{[\ce{NH3}]}{[\ce{NH4+}]} \\
\textrm{9.20} = 9.25 + \log \frac{[\ce{NH3}]}{[\ce{NH4+}]} \\
\frac{[\ce{NH3}]}{[\ce{NH4+}]} = 0.89
$$
So for every mole of $\ce{NH4+}$ I need $0.89$ moles of $\ce{NH3}$ to reach the desired pH of 9.20. I know that the buffer must withstand $0.004$ moles of $\ce{NaOH}/\ce{HCl}$, so I can set up the inequality
$$
8.70 < \textrm{pKa} + \log \frac{[\ce{NH3}]}{[\ce{NH4+}]} < 9.70 \\
-0.55 < \log \frac{[\ce{NH3}]}{[\ce{NH4+}]} < 0.45 \\
0.28 < \frac{[\ce{NH3}]}{[\ce{NH4+}]} < 2.82
$$
So I know the relative ratios I need to be within after the strong base and acid, but from here, how do I proceed with my $0.1\textrm{M}$ ammonia solution and ammonium chloride to get the desired ratio and buffer capacity? |
Creating a buffer with with a target pH and given weak base? |
Unfortunately I did not find a high resolution spectrum of this compound, which would have quickly answered your question.
Nevertheless, ionized alcohols and even more primary alcohols have a main fragmentation pathway which is the loss of water to yield an ionized alkene. In this case, the corresponding alkene would be 4-methyl-1-pentene, at *m/z* 84. The peak is present although rather small in the EI spectrum. From there, it is quite obvious, when one looks at the fragmentation spectrum of 4-methyl-1-pentene ([NIST Webbook spectrum][1]), that it shares a lot of similarities with the 4-methylpentan-1-ol EI spectrum. (See for instance peaks at *m/z* 69, 56, 43, 42, 41.) From there, it is quite likely that the *m/z* 56 peak is ionized isobutene ($\ce{C_4H_8}^{\bullet +}$) arising from a retro-ene type rearrangement.
[1]: https://webbook.nist.gov/cgi/cbook.cgi?ID=C691372&Units=SI&Mask=200#Mass-Spec |
Between an electrode and an electrolyte there exists an interfacial potential difference.
Many authors give the electrode potential to be the electric potential of the electrode relative to the electrolyte. I have a few problems with this, and was wondering whether anyone could help.
We define the electrode potential of SHE to be 0V. It is impossible to measure the interfacial potential difference, however nevertheless one certainly exists between the reference electrode and the solution. Are we saying that we define the interfacial potential difference of the SHE to be zero, and then have electrode potentials of other couples as potential differences measured relative to this difference?
To my mind, this cannot be right. Don't we just set our zero reference (i.e. one end of our voltmeter) of electric potential at the electrode of the SHE, and measure electric potentials of other electrodes relative to this?
Why do so many authors conflate interfacial potential differences and electrode potentials? Or am I missing something here? Thank you!
|
Between an electrode and an electrolyte there exists an interfacial potential difference.
Many authors give the electrode potential to be the electric potential of the electrode relative to the electrolyte. I have a few problems with this, and was wondering whether anyone could help.
We define the electrode potential of SHE to be 0V. It is impossible to measure the interfacial potential difference, however nevertheless one certainly exists between the reference electrode and the solution. Are we saying that we define the interfacial potential difference of the SHE to be zero, and then have electrode potentials of other couples as interfacial potential differences measured relative to this interfacial potential difference?
To my mind, this cannot be right. Don't we just set our zero reference (i.e. one end of our voltmeter) of electric potential at the electrode of the SHE, and measure electric potentials of other electrodes relative to this?
Why do so many authors conflate interfacial potential differences and electrode potentials? Or am I missing something here? Thank you!
|
Between an electrode and an electrolyte there exists an interfacial potential difference.
Many authors give the electrode potential to be the electric potential of the electrode relative to the electrolyte. I have a few problems with this, and was wondering whether anyone could help.
We define the electrode potential of SHE to be 0V. It is impossible to measure the interfacial potential difference, however nevertheless one certainly exists between the reference electrode and the solution. Are we saying that we define the interfacial potential difference of the SHE to be zero, and then have electrode potentials of other couples as interfacial potential differences measured relative to this interfacial potential difference?
To my mind, this cannot be right. Don't we just set our zero reference (i.e. one end of our voltmeter) of electric potential at the electrode of the SHE, and measure electric potentials of other electrodes relative to this?
Sergio Trasatti wrote this regarding electrode potentials,
> Equation (4.7) shows that the "electrode potential", as obtained in
> practice, does not measure the electric potential drop between the
> bulk of the metal and the bulk of the solution, but it is a more
> complex quantity which includes both electrical and chemical
> contributions.
Why do so many authors conflate interfacial potential differences and electrode potentials? Or am I missing something here? Thank you!
|
It appears that perhaps **water** may have symmetric hydrogen bonds between oxygen atoms, but it would take at least 60 GPa of pressure to make water to bond like that.
Article named very descriptively "[Compression of Ice to 210 gigapascals: Infrared Evidence for a Symmetric Hydrogen-Bonded Phase][1]" proves it:
> Protonated and deuterated ices ($\ce{H2O}$ and $\ce{D2O}$) compressed to a maximum pressure of 210 gigapascals at 85 to 300 kelvin exhibit a phase transition at 60 gigapascals in $\ce{H2O}$ ice (70 gigapascals in $\ce{D2O}$ ice) on the basis of their infrared reflectance spectra determined with synchrotron radiation. The transition is characterized by soft-mode behavior of the $\nu_3$ $\ce{O-H}$ or $\ce{O-D}$ stretch below the transition, followed by a hardening (positive pressure shift) above it. This behavior is interpreted as the transformation of ice phase VII to a structure with symmetric hydrogen bonds.
On the other hand, article "[The Hydrogen Bond in the Solid State][2]" mentions:
> First example of an $\ce{O-H-N}$ hydrogen bond with a centered position of
> the proton: pentachlorophenol/4-methylpyridine at 100 K characterized
> by neutron diffraction studies (...)
Unfortunately:
> Even very small chemical changes in the system lead to loss of the
> symmetry (...)
so symmetric hydrogen bonds can probably **exist also in very low temperatures**.
**References**
[Goncharov, A F; Struzhkin, V V; Somayazulu, M S; Hemley, R J; Mao, H K. Science 273.5272][3]
[Steiner, Thomas Angew. Chem. Int. Ed. 41 1 71][4]
[1]: https://www.gl.ciw.edu/static/users/rhemley/166GoncharovSci1996.pdf
[2]: http://onlinelibrary.wiley.com/doi/10.1002/1521-3773%2820020104%2941:1%3C48::AID-ANIE48%3E3.0.CO;2-U/pdf
[3]: http://science.sciencemag.org/content/273/5272/218
[4]: http://onlinelibrary.wiley.com/doi/10.1002/1521-3773%2820020104%2941:1%3C48::AID-ANIE48%3E3.0.CO;2-U/full?2-U/full |
> Why isn't then the reaction carried out at the highest possible temperature since the rate of reaction would be very high and the yield would be very high consequently as well?
The rate constant would be high, but that does not mean that the net forward rate is high. If you start without product, the initial rate would be high, but would drop to zero very quickly as equilibrium is reached. The equilibrium concentration of product would be very low at high temperature, as you said, so the yield would be very low.
If you had a very cheap and highly efficient process to remove product directly from the reaction vessel, you could run the reaction at high temperature. However, the product removal is slow and expensive (cool down the reaction mixture, remove ammonia, and reheat the remaining reactant to feed back into the reactor). Because this is costly, the reaction is run at a compromise temperature where at equilibrium, about 15% of the reaction mixture is product. |
[![Problem Statement][1]][1]
[1]: https://i.stack.imgur.com/xqicB.png
An isotopic variant of the molecule SF6 is S19F418F2, with the two 18F nuclei oriented axially, so that the 18F-S-18F angle is 180°and the four 19F nuclei form a square in a plane perpendicular to the 18F-S-18F axis.All of the bond lengths are equal. In the figure, the regions surrounding the 18F nuclei are shown in blue, and the regions around the 19F nuclei are shown in green.Two of the moments of inertia of S19F418F2 are identical, and the third is slightly larger:IA= IB= 2.9942 ×10-45kg m2IC= 3.0749 ×10-45kg m2. Wikipedia describes SF6 as an “extremely potent greenhouse gas.”
What is the symmetry number s of S19F418F2?
|
[![Problem Statement][1]][1]
[1]: https://i.stack.imgur.com/xqicB.png
An isotopic variant of the molecule SF6 is S19F418F2, with the two 18F nuclei oriented axially, so that the 18F-S-18F angle is 180°and the four 19F nuclei form a square in a plane perpendicular to the 18F-S-18F axis.All of the bond lengths are equal. In the figure, the regions surrounding the 18F nuclei are shown in blue, and the regions around the 19F nuclei are shown in green.Two of the moments of inertia of S19F418F2 are identical, and the third is slightly larger:IA= IB= 2.9942 ×10-45kg m2IC= 3.0749 ×10-45kg m2. Wikipedia describes SF6 as an “extremely potent greenhouse gas.”
What is the symmetry number s of S19F418F2?
I have considered it and think there is one 4-fold axis, but cannot figure out how many that counts for or how to do the 3-fold or 2-fold axes.
|
Normally protein coordinates are generated from electron density, such as that from X-ray scattering experiment. In my case, I want the reverse - PDB to electron density mesh. I thought it was more trivial and a program should be available. But Google did not give me any luck.
Is there any existing python library/program which converts protein coordinate (pdb) into electron density mesh (custom resolution)? If not, how should one proceed? The orbital and atomistic electron density varies among atom types.
Your suggestion appreciated.
Edited:
The precision of electron density I am interested in is ~ 1-2A so hopefully DFT level might not be necessary in my case. The aim is to *visually resolve* sidechain atoms. Since there could be manipulation of the PDB upstream, some crystal structure information could be lost.
Indeed the raw electron density might provide such information but a unified treatment of PDB coordinate homogenizes structures, making a more fair comparison between them, specifically in my case. |
[![Problem Statement][1]][1]
[1]: https://i.stack.imgur.com/xqicB.png
An isotopic variant of the molecule SF$_6$ is S$^{19}$F$_4^{18}$F$_2$, with the two $^{18}$F nuclei oriented axially, so that the $^{18}$F-S-$^{18}$F angle is 180°and the four $^{19}$F nuclei form a square in a plane perpendicular to the $^{18}$F-S-$^{18}$F axis. All of the bond lengths are equal. In the figure, the regions surrounding the $^{18}$F nuclei are shown in blue, and the regions around the $^{19}$F nuclei are shown in green.Two of the moments of inertia of S$^{19}$F$_4^{18}$F$_2$ are identical, and the third is slightly larger: I$_A$= I$_B$ = $2.9942 ×10^{-45}$ kg m$^2$ and I$_C$= $3.0749×10^{-45}$ kg m$^2$. Wikipedia describes SF$_6$ as an “extremely potent greenhouse gas.”
What is the symmetry number of S$^{19}$F$_4^{18}$F$_2$?
I have considered it and think there is one 4-fold axis, but cannot figure out how many that counts for or how to do the 3-fold or 2-fold axes.
|
[![Problem Statement][1]][1]
[1]: https://i.stack.imgur.com/xqicB.png
An isotopic variant of the molecule SF$_6$ is S$^{19}$F$_4^{18}$F$_2$, with the two $^{18}$F nuclei oriented axially, so that the $^{18}$F-S-$^{18}$F angle is 180°and the four $^{19}$F nuclei form a square in a plane perpendicular to the $^{18}$F-S-$^{18}$F axis. All of the bond lengths are equal. In the figure, the regions surrounding the $^{18}$F nuclei are shown in blue, and the regions around the $^{19}$F nuclei are shown in green.Two of the moments of inertia of S$^{19}$F$_4^{18}$F$_2$ are identical, and the third is slightly larger: I$_A$= I$_B$ = $2.9942 ×10^{-45}$ kg m$^2$ and I$_C$= $3.0749×10^{-45}$ kg m$^2$. Wikipedia describes SF$_6$ as an “extremely potent greenhouse gas.”
What is the symmetry number of S$^{19}$F$_4^{18}$F$_2$?
I have considered it and think there is one 4-fold axis, and two 2 fold axes, but still unsure if that is right
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Yes, do use household dilute H2O2 but, in general, do not use commercial percarbonates powders as they can contain an additive to convert the friendly percarbonate into more powerful Peracetic acid (PAA). The latter allows the otherwise weak bleaching power of the H2O2 to compete with chlorine-based bleaching. However, this comes at a price (safety). Hence, the dire warning labels, usually in at least two languages, on Oxi-Bleach and generic related products.
I quote myself on this subject:
>Sodium percarbonate is chemically just an addition compound of Na2CO3 and Hydrogen peroxide.
>Also, while Sodium carbonate and Sodium percarbonate (basically Na2CO3 and 3Na2CO3.2H2O2) are often listed as the main ingredients in typical chlorine free bleach, an additive, TAED, which acts as a key activator ([see, for example]( https://en.m.wikipedia.org/wiki/OxiClean)) is not even listed on the label. TetraAcetylEthyleneDiamine is apparently commonly employed as a bleach activator in many laundry products ([see this](https://en.m.wikipedia.org/wiki/Tetraacetylethylenediamine )). TAED reacts with H2O2 in alkaline conditions (referred to as perhydrolysis) creating, in part, Peracetic Acid. The latter PAA is actually preferred over sluggish H2O2 for bleaching. In other words, it is not the H2O2 as the active bleaching agent, but PAA created in situ. So, other than possibly misleading implying that eco friendly hydrogen peroxide is the active agent, it is, in reality, PAA, a probematic compound with associated health concerns (see Marquand, E. C.; et al. , 2007. "Asthma Caused by Peracetic Acid-Hydrogen Peroxide Mixture". J. Occup. Health. 49 (2): 155–158.). Here is a MSDS on an actual PAA mix ( 76-61% water, PAA 20-35%, 3% Acetic acid and 1% H2O2) [available at](https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.peraceticacidsystems.com/downloads/msds.pdf&ved=0ahUKEwiFiJ_e4brTAhUBTSYKHWNSDK8QFggcMAE&usg=AFQjCNHQDWuC2ZCKmHPR4hvSdl3eJTVI2w&sig2=J4EcGfXW-06p54ggP_Q9TQ) which is far from friendly but does eventually totally decompose into harmless O2, CO2, H2O,...
>As such anyone using a commercial percarbonate product should at least be aware of safety issues and that one is likely employing a Peracetic acid mix.
However, such more powerful PAA based mixtures do have their use and is recommended by the U.S. Military as a chemical/biological warfare decontamination protocol (see ["Development of Bicarbonate-Activated Peroxide as a Chemical and Biological Warfare Agent Decontaminant"](https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.dtic.mil/dtic/tr/fulltext/u2/a455611.pdf&ved=0ahUKEwi8yM-QrLPXAhVFeCYKHWMKDSkQFgg9MAM&usg=AOvVaw0DyOiHVg-2Rh2AnPEJri3b)). So, it is up to the user to weigh the relative risks of the situation.
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I need to create a $100\textrm{mL}$ buffer of $\textrm{pH = 9.20}$ with ammonia and ammonium chloride such that $\textrm{pH = }9.20\pm0.50$ with $20\textrm{mL}$ of $0.2\textrm{M } \ce{NaOH}/\ce{HCl}$. I am provided with $0.1\textrm{M}$ ammonia and ammonium chloride salt.
I used the Henderson-Hasselbalch equation to figure out the relative amounts of $\ce{NH3}$ and $\ce{NH4+}$ I need:
$$
\textrm{pH} = \textrm{pKa} + \log \frac{[\ce{NH3}]}{[\ce{NH4+}]} \\
\textrm{9.20} = 9.25 + \log \frac{[\ce{NH3}]}{[\ce{NH4+}]} \\
\frac{[\ce{NH3}]}{[\ce{NH4+}]} = 0.89
$$
So for every mole of $\ce{NH4+}$ I need $0.89$ moles of $\ce{NH3}$ to reach the desired pH of 9.20. I know that the buffer must withstand $0.004$ moles of $\ce{NaOH}/\ce{HCl}$, so I can set up the inequality
$$
8.70 < \textrm{pKa} + \log \frac{[\ce{NH3}]}{[\ce{NH4+}]} < 9.70 \\
-0.55 < \log \frac{[\ce{NH3}]}{[\ce{NH4+}]} < 0.45 \\
0.28 < \frac{[\ce{NH3}]}{[\ce{NH4+}]} < 2.82
$$
So I know the relative ratios I need to be within after the strong base and acid, but from here, how do I proceed with my $0.1\textrm{M}$ ammonia solution and ammonium chloride to get the desired ratio and buffer capacity? |
I’m currently investigating a method to chemically pretreat cellulosic waste as bisorbents for enhanced uptake of lead in water. I intend to measure the initial and final concentration of water to record the change in concentration of aqueous lead via a chelatometric titration.
In my experiment, I’ll be performing filtration in the batch mode at three different initial concentrations (5 mg/L, 20 mg/L, 50 mg/L). To visualize the magnitude of these concentrations, I’ve converted the units to the more conventional mol/L (M).
[Initial concentrations of water samples I’ll be testing on in mol/L (M)][1]
My question is, are these initial concentrations too low to be conducting a titration on. If so, what would be a good initial concentration of lead to be working with (considering after filtration, the concentration of lead will diminish significantly). If these initial (and very small post filtration) concentrations are measurable for a titration, what is a good concentration for the EDTA titrant. Should the titrant concentration be significantly less than the analyte concentration?
All the best!
[1]: https://i.stack.imgur.com/1mrRq.jpg |
Sorry to tell you a bad news. Classical methods, like titrimetry or gravimetry do not work very well at low concentrations. Failure would be a strong word. The beauty of EDTA is that it forms 1:1 complex with most metals. Pb is not an exception. If your lead solution is 0.000001 M, your EDTA solution should be 0.000001 M. Such concentrations are never recommended in classical methods.
For ppm level, spectrophotometric methods can work quite well. Go to Google Scholar and search the methods in [Google Scholar][1]
[1]: https://scholar.google.com/scholar?hl=en&as_sdt=0%2C44&q=spectrophotometric%20determination%20of%20lead&btnG= |
What happens to the intramolecular bonds when a network covalent substance is melted? I understand that in covalent molecular substances, the intermolecular bonds weaken between the molecules once molten. My confusion is with what happens to the bonds between network covalent substances when melted.
- Do the intramolecular bonds break, leaving only the individual atoms (carbon for example in graphite or diamond).
- Do the intramolecular bonds weaken
The basis for this query is when I was asked to predict the electrical conductivity of graphite and silicon dioxide in molten states (Graphite sublimates, but under pressure is liquid). I started by researching the atomic and bonding structure of the elements when they are melted but could find very little information.
TLDR: What happens to covalent network bonds when they melt
Thankyou
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With the Coronavirus in full swing around the globe, I wanted an answer to this, particularly since my dad has just been diagnosed with Leukaemia.
We can't find hand wash anywhere but instead I just bought some Radox shower gel and put that in a hand soap bottle.
Is there a significant difference between hand soap and shower gel when it comes to killing off germs/viruses? Or is the case that both are detergents and it's all around marketing? |
Is there a difference between hand soap and body soap with killing viruses? |
It's given in text that "Electrode potential among other things depends upon: enthalpy of sublimation,ionization enthalpy and hydration enthalpy." I could understand why it would depend upon ionization enthalpy as less is the IE easily we could remove the electron thereby reducing the other reactant. But I couldn't figure out why the other two enthalpy comes. But after some thinking I thought maybe we are adding the enthalpy of the three with sign and substituting in ∆G°=∆H°-T∆S° and obtaining ∆G° to substitute in ∆G°=-nFE°cell to find E°cell value. I couldn't think further clearly after this. Could you help me? ( I'm trying to understand why lithium because of its high hydration enthalpy overweighs its high ionization enthalpy and becomes the strongest reducing agent in aqueous solution) |
Why does electrode potential depend upon enthalpy of hydration and sublimation? |
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