texts: Does alumina become transparent at high temperatures?

texts:
Consider a normal opaque alumina crucible. I've heard that they become transparent at higher temperatures and therefore, are not appropriate for high precision DSC (caloric) measurements. The reason is, that there might be a lack of energy due to radiation losses (in addition to the bad thermal conductivity).

I was not able to find at least one quotable source for this claim. So my two questions are:

Is this actually right?
Does someone know of a quotable source for this (scientific papers, textbooks, etc...)?

Thanks!

Edit: Based on my research, the absorption rises with temperature, so the transparency should degrease, what is a somewhat contradictory to A.K. answer, isn't it?


texts:
What state of matter are phosphomonoesterases?  I am not a biochemist; while I've found various lists of such enzymes, and plenty of (to me) barely comprehensible articles describing their production, it's not clear to me whether the final product in isolation is a solid, liquid, or gas.

More generally, is there some reference work in which one can look up the state of matter (at standard temperature and pressure) for a given chemical?


texts: Why is Electrostatic Potential Energy positive when the charges are like?

texts:
We know that in an atom charge of an electron at infinity is zero. As it approaches the nucleus it become more and more negatively charged.
We also know that E.P.E is positive when charges are like and negative when charges are opposite.
Well does it mean that as an electron approaches nucleus there is repulsion which causes the approaching electron to go away. As the electron go away it is getting closer to to infinity point because of which electron become less and less negatively charged. So the E.P.E is positive .Nucleus of atom is like earth and the electron are objects.The farther the object move from earth it has more Potential energy.


texts: What are some uses for an O2/N2 mixture that is more N2-rich than air?

texts:
What are some uses for an $\ce{O2}$/$\ce{N2}$ mixture that is more $\ce{N2}$-rich than air?
I need help with this, my professor did not do a good job explaining it, and I can't find a source to read about it.


texts: How do technicians treat spilt mercury and bromine?

texts:
As we know, mercury and bromine are in liquid state at room conditions and they are hazardous. The technicians should have ways to treat them if they are spilt.

  How can we safely treat spilt $\ce{Hg}$ and $\ce{Br}$?

I have thought of using dry ice to cool the mercury down into a solid, which can then be easily removed. But I do not think that this is really practical. Maybe some chemical reactions can help to somehow convert the them into a solid in order to remove them.


texts: How do we get rid of dangerous explosive acetone peroxide and nitroglycerine?

texts:
Imagine the police (or army or whoever's job is that) found out that some maniac placed a lot of primary explosives under a building. They have evacuated the building and deactivated the trigger.

What now? You have a barrel full of Acetone peroxide (terrorist's favourite explosive). You move it - it might blow.

Even if it doesn't - can you react acetone peroxide slowly, to avoid explosion?

What do factories do with this compound formed as a side waste?

Could you answer the same for nitroglycerine?


texts: I am not sure where to begin with this problem. I feel Br carries negative charge and is this gonna be no reaction since the alpha carbon is $sp^2$?


texts:
I was wondering why when acetaldehyde is treated with $\ce{OH-}$, the $\ce{OH-}$ will attack the methyl group instead of the carbonyl carbon, forming an enolate anion. I would have though that the $\ce{OH-}$ would have attacked the carbonyl carbon due to it having a  relative positive charge.

Additionally, my professor said during lectures that form x is favored over form Y. Is this because a negative oxygen is able to delocalize the negative charge (and be protonated more easily) more efficently than a $\ce{CH2-}$ group? If so,  is the x form so dramatically favored that it would not make sense to draw any mechanisms involving the y form?


texts: What's the difference between HOMO-LUMO and valence-conduction bands?

texts:
From Wikipedia:

  Roughly, the HOMO level is to organic semiconductors what the valence
  band maximum is to inorganic semiconductors and quantum dots. The same
  analogy exists between the LUMO level and the conduction band minimum.

Why such distinction even exists? If it's the same physical concept, why use different names?


texts: Relative acidities of alkanes, alkenes, and alkynes

texts:
How does one explain the trend in bond lengths and acidity of the following hydrocarbons?

$$\begin{array}{ccc}
\hline
\text{Species} & \ce{C-H}\text{ bond length / Å} & \mathrm{p}K_\mathrm{a} \\
\hline
\text{Ethane, }\ce{C2H6} & 1.102 & 50 \\
\text{Ethene, }\ce{C2H4} & 1.085 & 44 \\
\text{Ethyne, }\ce{C2H2} & 1.061 & 25 \\
\hline
\end{array}$$

Shouldn't the shorter bonds between $\ce{C-H}$ be easier to break than longer ones, making ethane the most acidic?


texts: Is gravity an obstacle for homogenous solvation due to diffusion?

texts:
If you have a glas with a spoon of salt ($\ce{NaCl}$) in it and you carefully add the water($15^\circ\mathrm{C}$). A lot of the salt will not be dissolved immediatelly, it will take a while for full dissolution.

When the salt dissolves, it is said that the salt is mixed equally in the water. But $\ce{NaCl}$ is split in two ions $\ce{Na+}$ and $\ce{Cl-}$. $\ce{Cl}$ has a mass of $35$ and Na $23$. But due to gravity (or is really curved space in the glass a better word) you should expect that the $\ce{Cl}$ atom will be more at the bottom then the $\ce{Na}$ ion. Is that right or is there someting I'm missing?

So can you say that after an hour the salt is evenly diffused through the water and that there are probably more more $\ce{Na+}$ ions at the top of the glass, so that the top of the salt water will taste more salty due to presence of sodium, which has more power of giving salty tast?


texts: How to predict the basicity of organic amines?

texts:
The following compounds were given, and I have to predict their order of basicity:

\begin{align}
\text{guanidine} &: \ce{(H2N)2C(NH)} \tag{A}\label{guanidine}\\
\text{acetamidine} &: \ce{(H3C)(H2N)C(NH)} \tag{B}\label{acetamidine}\\
\text{benzamidine} &: \ce{(H5C6)(H2N)C(NH)} \tag{C}\label{benzamidine}\\
\text{dimethylamine} &: \ce{(H3C)2NH} \tag{D}\label{dimethylamine}
\end{align}

After nitrogen donates a lone pair to $\ce{H+}$ in option \eqref{guanidine}, it has 2 resonance structures, whereas in option \eqref{benzamidine}, after donating a lone pair to $\ce{H+}$, it has 4 resonance structures. Therefore \eqref{benzamidine} should be the most basic or should have the highest rate of protonation. The answer given is option \eqref{guanidine}.
Whereas \eqref{acetamidine} and \eqref{dimethylamine} have 1 and 0 resonating structures, so the main confusion is between option \eqref{guanidine} and \eqref{benzamidine}.


texts: What is the lowest mass measurable using a 4 decimal point analytical balance?

texts:
I think it is 1 mg, but I've heard people saying 0.1 mg. As 0.1 mg = 0.0001 g, which is the uncertain digit, I think such a measurement is not reliable at all.

Any opinions ? Thanks.


texts:
This equation describes the total current in bulk solution in a battery caused by migration in the electrolyte.

Then the source says what A is: In the bulk solution (away from the electrode), concentration gradients are generally small, and the total current is carried mainly by migration. All charged species contribute. For species j in the bulk region of a linear mass transfer system having a cross sectional area, $A$...

$$i = \sum_j i_j = \frac{FA\,\Delta E}{l} \sum_j |z_j| u_j C_j$$

I am confused if $A$ is the electrode area or the solution cross sectional area.

I will describe what the rest of the variables are

The $i$ is the current in the bulk solution.
F is Faraday's Constant
∆E is the change in potential (i.e. Voltage measurement of the battery)
l is the distance of how far the electrodes are separated (or at least that is what I think)
z is the charge of species j
u is mobility of species j
C is the concentration of species j


texts: method of separating product and conserving the catalyst

texts:
I'm looking for a way to separate reaction product of iodobenzene with ethyl 2-methyl-3-oxopentanoate in 1,4-dioxane (toluene is an alternative as a solvent). The catalyst being used is Pd2(dba)3 with Ph3P as a ligand and K3PO4 as a base.

I was thinking about fractional distillation under partial vacuum because there's a risk of explosion if there's some leftover unreacted iodobenzene heated to high temperatures.

Provided the liquids distil off, the reaction flask should be left with some solid junk containing Ph3P+Pd2(dba)3 and K3PO4. Then this mixture could be washed with water to get rid of K3PO4, KI, water-soluble side products and dry the catalyst+ligand under vacuum and use it again in another run.

So, is it possible for me to separate the product from the liquids using distillation and to reuse catalyst with the procedure I proposed?


texts: Regarding Clemensen Reduction of the following compound

texts:
While I was doing problems on reduction of aldehydes and ketones, I encountered this particular question

Here, I know that Clemensen reduction reduces the ketone group to $-CH_2-$ group. But, the answer key has given the option (c). I also know that the mechanism for this reduction is still shaky for the senior high school kid. But, how to deal with substitution like these as in case of this question

In this question option (a) is the answer though this is wolf kishner reduction.

Any suggestions how to solve these reactions?


texts: Shouldn't the pH at the equivalence point always be 7?

texts:
I learned in class that the equivalence point in an acid-base titration is reached when the solution contains an equal amount of substance of $\ce{OH-}$ and $\ce{H+}$ ions. However, in a weak acid and strong alkali titration, the pH at the equivalence point (when I added the right amount of acid and alkali to make it a neutral solution) is 9. Also, in the titration of a strong acid and weak alkali, the pH of the solution when I have added the correct amounts is 5.

My question:

If I add 1 mole of ethanoic acid to 1 mole of sodium hydroxide, I should get a neutral solution and the pH should be 7. However, why is the pH 9? This does not make sense to me as a pH 9 suggest that the concentration of $\ce{OH-}$ is higher than the concentration of $\ce{H+}$. But how is that, I reacted the correct amounts?


texts: Z effective is the net positive charge experienced by an electron. But what is the unit of this net charge: coulomb (C) or microcoulomb (μC), or something else?


texts:
I wanted to ask clarifications about a passage in Atkin's physical chemistry book, chapter 9, in the paragraph 9.2 description of equilibrium.

For studying equilibrium of a reaction, where $\nu_i$ are the stechiometric coefficients it imposes $\sum_i \nu_i \mu_i=0$ with $\mu$ the chemical coefficients. At this point it writes the chemical coefficients as a function of the activities $\mu_i=\mu_i^\circ+RT\ln(a_i)$ and identifies the term $\sum_i \nu_i \mu_i^\circ$ with the standard reaction Gibbs energy. I do not understand this identification. I thought that the standard state for the definition of activities (even dependent on wether the substance is a solute or a solvent) was not the same reference state for computing the reaction Gibbs energy (and does not depend on the role played by the substance in the reaction). I'm surely getting something wrong...


texts: Difference between 18 electron rule and effective atomic number rule

texts: Is there any difference between 18-electron rule and effective atomic number rule? Both rules are based on attainment of a noble gas configuraion as a criteria for stability of complexes. Besides, both rules were proposed by Sidgwick. I was wondering if the mere fact that 18-electron rule applies mainly to organometallic complexes is a good enough difference.


texts: Is benzocyclobutadiene aromatic or anti-aromatic?

texts: My teacher told that benzocyclobutadiene is both aromatic and anti-aromatic. I do not understand why. Can anyone explain?


texts: Does Genistein remain in resonance stabilised form in physiological pH or acidic pH?

texts:
As a follow up, does the Carbonyl group at 4 position group get deprotonated or Hydroxyl group at 5 position get deprotonated? How does the resonance structure look? I have been looking through literature but have not been able to find any reference to this.
Does the deprotonation start with the carbonyl group or does it always have to start with hydroxyl group?
I may not sound clear as I am an amateur when it comes to organic chemistry.


texts: Why does CCl4 not undergo hydrolysis while other chlorine-derivatives of methane do?

texts:
In one of my textbooks, I came across a question as to why does $\ce{CCl4}$ not undergo hydrolysis. The answer given went along the lines of carbon lacking a vacant d-orbital to accept the lone pair of oxygen from water.
However I was curious to find out that other chlorine-derivatives of methane i.e. $\ce{CH3Cl}$, $\ce{CH2Cl2}$ and $\ce{CHCl3}$ (to some extent) do undergo hydrolysis, even though carbon lacks the vacant d-orbital.(Mechanism involved I figured would be Lone pair of oxygen attacking the vacant anti-bonding molecular orbital of carbon)
What is the actual reason that carbon tetra-chloride doesn't undergo hydrolysis while its other chlorine-derivatives seem to undergo hydrolysis effectively?
My only logical approach was the large size of chlorine provides stearic hindrance towards the attacking lone pair of water, But I didn't find any substantiation for this.
A detailed explanation would be appreciated! thanks in advance!


texts: Why is FORTRAN so commonly used in computational chemistry?

texts:
I've been using Ruby to write scripts for research, but I want to get into some heavier stuff that Ruby is just too slow for. I noticed there are a few things written in C and C++, but there is an oddly large proportion of software used in computational chemistry that is written in FORTRAN (in which I have zero experience.)

Why is FORTRAN used in computational chemistry? From what I understand, FORTRAN is kind of on the ancient side (“punchcard” old.) I was a bit shocked to find fairly recently written tutorials for FORTRAN.

Is it a sort of, "this is how we've always done it," thing or is there an efficiency aspect to FORTRAN I'm overlooking?

Note: I may have FORTRAN confused with later programming languages with similar names.


texts: Stirring the reaction between hydrochloric acid and a powdered substance

texts:
For an experiment, I'm adding several substances (as powders) to hydrochloric acid, and measuring the temperature changes to calculate enthalpy. However when adding the powders, the mixture requires some stirring to get all of the substance reacting.

As I am measuring temperature via a temperature probe hooked up to a data logger (to obtain a temp. against time graph), I need a way to briefly stir the mixture in a controlled way that won't affect the change in temperature (reactions are both endo and exothermic). I have tried stirring with the probe itself, but this is not ideal as the probe is pretty sensitive and friction/bumping with the side of the vessel may affect the recording.

I initially looked at a magnetic stirring to obtain uniform and controlled stirring, but then I realized the magnet would absorb heat and potentially increase the temperature of the mixture through kinetic energy. So I'm after a stirring method that will not affect temperature, so that the temperature change I record is solely due to the reaction.

Any suggestions are welcome, because I can't think of any tool or method that would suit.


texts: Nomenclature of a Benzopyran (Chromene) as a Substituent of an Aldehyde

texts:
I am currently writing a paper on the benzopyran above.
I am attempting to name the compound using IUPAC conventions. Because there is an aldehyde moiety, I suspect I will need to name the compound as a substituent of methanal (so 1-(substituent name)methanal). I could alternatively name the aldehyde as a formyl moiety, but this would not be following IUPAC priorities. Benzopyrans have the following locants (with the 2H indicating an extra hydrogen at the 2 position). So, because the aldehyde is at the 6th locant, the compound would be named 1-(XXXXX-6-yl)methanal. The substituents on the benzopyran are as follows

2,2-dimethyl
2,7-dimethoxy
8-(1-oxo-butyl)

By assembling the everything in order, I get:
1-(5,7-dimethoxy-2,2-dimethyl-8-(1-oxo-butyl)-2H-1-benzopyran-6-yl)methanal

I am not sure whether or not I should have named this compound based on the aldehyde moiety since it would be so trivial to name it as a formyl substituent instead?


texts: Why do highly branched alkanes have higher octane numbers than their corresponding linear isomer?

texts: The octane number of fuels are based on a set of primary reference fuels, which are mixtures of iso-octane and n-heptane. Now iso-octane being branched alkane has very less tendency to react and given ON=100 and n-heptane reacts easily and given ON=0. However n-octane that is the corresponding linear isomer of iso-octane has an ON<0. Now why does branching in a alkanes reduce its reactivity?


texts:
When cooking oatmeal (rolled oats, either long-cooking or instant) on the stove or in the microwave, when it reaches the boiling point, if left unchecked it will quickly "grow" and overflow the container in which it is cooking, even if it is a very large container.

A comparable amount of water boiling in the same pot or container would not do this.  It would boil, yes, but it would not "grow" and overflow the container.  I have not seen this happen with other grains.

Why does oatmeal do this?


texts: If polyethylene glycol (PEG) is hygroscopic, how does it protect wood?

texts: Archaeologists and conservators use polyethylene glycol (PEG) to replace water inside wood to protect it from shrinking and expanding with changes in humidity. But it is hygroscopic—even more so than wood, it sounds like. So how does it work? Is it like the polymer in a diaper that is able to hold on to moisture and therefore not allow any additional moisture to expand the wood further? Or is it simply filling in all the holes and its hygroscopic character is inconsequential?


texts: Why are there peaks in electronegativities in d-block elements?

texts:
Looking at the Pauling electronegativities in the Periodic Table (below, from ChemWiki):

Asides from the overall trend of increasing electronegativity across and up the Periodic Table (towards fluorine), there seems to be a minor peak in the first 3 periods of the $d$-block elements, this peak becomes more pronounced as you go down the $d$-block, with the most noticable peaks in Periods 5 and 6 - seemingly the reverse of the overall trend. This is shown in the graph below (Image source):

In the ChemWiki page, there is also a reference to the Allred-Rochow Electronegativity Scale, which also has peaks occurring most prominently in Periods 4 and 6:

Image source

The Wikipedia page Electronegativity details several methods of calculation, which brings into question how well-defined the electronegativity values are; however, there still seems to be the peaks occurring, particularly in Periods 5 and 6, and to a lesser extent in Period 4.

What is the reason for these electrongativity peaks in the $d$-block?


texts: Can 1,3,5-trihydroxybenzene perform haloform reaction?

texts:
As far as I know it's not possible for 1,3,5-trihydroxybenzene to give the haloform reaction.

The prerequisites(that I know) for the haloform reaction are:

Only those organic compounds which can be converted to a methyl ketone or acetaldehyde by means of oxidation (by $\ce{NaOX}$ ($\ce{NaOH + X2}$) type agents which are present in the reaction mixture) give this reaction. And obviously a methyl ketone or acetaldehyde would give this reaction too.

So the problem is I don't see how  1,3,5-trihydroxybenzene meet those prerequisites. Is there any way out because in a recent practice test I came to know that 1,3,5-trihydroxybenzene does give the haloform reaction.


texts:
I am getting confused between the type of mesomeric effect (+M or -M) shown by compounds containing $\ce{-COX}$ where $\ce{X}$ is an electronegative element.

Examples: $\ce{-CONHCH3}$, $\ce{-COOCH3}$, $\ce{-COOH}$.

According to me, all these compounds must show both a +M as well as a -M effect. Since the group (e.g. $\ce{-COX}$) can accept as well as donate $\pi$ electrons (as in $\ce{CH_2=CH-COOH}$).

However, the book says these compounds show only -M effect. Please explain me the reason behind it.

In the above example, isn't the group showing +M effect, since it's donating the electrons?


texts: Uncertainity principle of a particle on a ring in $m=0$ state

texts:
When a particle is on a ring, we know that the commutator $[L_z,x]=i\hbar y$ and $[L_z,y]=-i\hbar x$. So we can't measure $L_z$ and $x$ & $L_z$ and $y$ simultaneously with infinite accuracy.
When $m=0$, then the energy of the particle is 0. So we can say that $L_z$(angular momentum in z-direction) is 0 as we consider potential energy to be 0 on the ring. This also implies $p_z$ is also zero as $L_z=rp_z$.
My question is that if the particle is in $m=0$ state on the ring, then if we find its position $x$ and $y$ simultaneously {as $[x,y]=0$}, we are confident that $L_z=0$ on the ring.
Then doesn't the commutator relation for $[L_z,x]=[L_z,y]=0=[p_z,z]$ (as $z=0$ is considered on ring) for $m=0$?
Here we see that commutator relation and uncertainty principle is violated. I know that it can't be the case as they are generalized. Please tell me what is wrong in my reasoning.


texts: I recently learned about the MO bonding model in metals, where many metal atoms form lots of orbitals close in energy that form bands. However, I can't understand the bonding in d10 metals. It seems to me that if they form MOs, then the bonding and antibonding orbitals will both be filled, resulting in net zero bonding. The d10 metals obviously bond anyway, so what is wrong with my reasoning?


texts: Is there wavefunction interference between alternate reaction pathways?

texts:
I'll give a specific example to clarify my question. If we look at the approach of chloromethylenecarbene's electron pair to cis-2-butene in the reaction of creating 1-chloro-2,3-dimethylcyclopropane, there's a symmetry in the choice of where the nucleophilic attack can happen.

These two alternatives can be represented by wavefunctions and so I would expect there to be an interference effect between them that would make the reaction different than if one of the spots was somehow unavailable for reaction (perhaps by the existence of some electron donating/withdrawing groups or other hindering groups attached on the periphery of the butene's double bonds).

Has reaction pathway alternatives interference been observed?


texts: Why doesn't natural gas combustion release only one-sixth as much carbon dioxide as coal burning?

texts:
Burning hydrogen releases a little more energy than burning carbon, correct?

And methane is CH4, but coal is mostly C, correct?

So shouldn't burning pure carbon release five times the CO2 (Assuming combusting carbon releases the same energy as hydrogen), or even six times per unit energy 'released'/'created' by the power plant (since hydrogen is more energy-dense per unit mass than carbon)?


texts: I'm not a chemist but something of a tinkerer and adult boy scout.  Currently if you want to make soap, you need fat and lye.  Fat I'm good with, it's easy to get and you can even get it from plants. Lye usually requires wood ash though and that I would rather avoid, if possible. If not possible and burning something is mandatory, then I want the biggest bang for my buck. That means I want to get the most lye I possibly can with the least pollutant release, especially greenhouse gasses and we shouldn't be thinking of just wood. Anything that will get us some low impact soap in the end. We may even want to replace soap as an idea with something else that you can make at home and wash humans, clothing and dishes with.


texts: Meso and achiral does both term means the same?

texts: When a molecule has plane of symmetry,  or centre of symmetry it is termed as an  achiral compound (though it contain some chiral centres).  Same goes for the meso compounds due to the internal compensation.  So both terms mean exactly same.  But I am eager to to know the applications of these terms  in different cases.  All meso compounds can be told achiral and as well as all chiral compounds as meso?


texts: What trends affect hydrophobicity in amino acids?

texts: I was wondering if the length of the carbon backbone affects hydrophobicity of amino acids (i.e. longer carbon backbone of side group = less polar = more hydrophobic).


texts: Minimising the formation of manganese dioxide in the titration of potassium permanganate

texts: For a titration of potassium permanganate into a standard acidified solution of hydrated iron (II) ammonium sulfate, the solution seems to end up brown (due to the formation of manganese dioxide) during the titration unless the titration is carried out extremely slowly. How can I minimise this? Adding sulfuric acid to the solution seemed to help, but is there a physical way to prevent manganese dioxide forming when the titrant is added too rapidly?


texts: Calculating the amount of a product at the reaction equilibrium

texts:
$\ce{Cr2O3}$ can be reduced to the elements chromium with high temperature and carbon by this two reactions:

$$
\begin{align}
\ce{Cr2O3(s) + 3C(s) &-> 2Cr(s) + 3 CO(g)} \label{rxn:1}\tag{1}\\
\ce{Cr2O3(s) + \frac{3}{2}C(s) &-> 2Cr(s) + \frac{3}{2}CO2(g)} \label{rxn:2}\tag{2}
\end{align}
$$

The following image shows the equilibrium constants.

Using the image, we can get $K_1$, $\Delta_rG^\circ_1$, $\Delta_rH^\circ_1$, $\Delta_rS^\circ_1$ of reaction $\eqref{rxn:1}$ as well as $K_2$ for $T = 1500\,\mbox{K}$.

Assume all of them are given. Now:

In a closed container with $V = 1.00\,\mbox{dm}^3$ inner volume, we put $5.00\,\mbox{g}$ of $\ce{Cr2O3}$ and $20.0\,\mbox{g}$ carbon. For $T = 1500\,\mbox{K}$ we have the reaction equilibrium $\eqref{rxn:1}$ and $\eqref{rxn:2}$.

Problem: What mass (in g) reduced chromium do we have in the equilibrium?

Question: Now I don't know how to solve the problem. I can do everything above like determining the Gibbs-Energy or the equilibrium constants, but what are my though now to get the amount of reduced chromium?

First, I don't get exactly what it means if they say "in the equilibrium". Does that refer to $\eqref{rxn:1}$ or $\eqref{rxn:2}$ or both?

Further, how do I actually calculate it?


texts: How can scientists measure the electron affinity and the ionization energy of an element?

texts: I am pretty curious about the method that the scientists use to measure the electron affinity and the ionization energy of an element. If someone knows about it, please tell me.


texts: 3,4-Methylenedioxyamphetamine (MDA) basic extraction

texts: At my lab we perform a basic extraction of seized MDA with $\ce{NaOH}$ $\pu{2M}$ prior to GC/MS analysis.  $\ce{MDA + NaOH -> MDA- + Na+ + H2O}$. This reaction should favor the products since $\mathrm{p}K_\mathrm{a}$ of MDA is about 10 and $\mathrm{p}K_\mathrm{a}$ of $\ce{H2O}$ is about 16. All of the MDA should be converted to its ionic form which is soluble in the aqueous layer. Why is there still enough of MDA in the organic layer ($\ce{CHCl3}$) to be detected by GC/MS?


texts: Alkenes express different reactivity with acids depending on concentration and temperature

texts:
The below images show when 1-butene reacts with different reagents (in d it's also H2SO4 not H2SO). My question is why are the two products different?

I can get that in c), because it's more dilute there's more water to act as the nucleophile, and in d) there's more H2SO4 so that would act as the nucleophile but what's the role of temperature?


texts: Are groups other than carbonyl reduced by Clemmensen reduction?

texts:
According to my textbook, Clemmensen reduction reduces only aldehydes and ketones to alkanes. But in this question:

$\ce{Zn-Hg/HCl}$ has reduced both the ketonic and nitro group. Correct answer given is D.

So, what exactly is this reduction's mechanism? Is it an exception? If not, why isn't it stated in the books alongside the carbonyl groups?


texts: Does this wire gauze contain asbestos? Can I tell visually?

texts: I bought a wire gauze which claimed to be made of ceramic, and asbestos-free. However, I bought it from Amazon (not a trustworthy source), and I see fibers around the edge of the center. Is there a way to tell whether this is asbestos?


texts: Question about reversible chemistries in anode and cathodes

texts:
I've been reading a lot about cathode and anode chemistries recently involving Li-ion cells and solid state chemistries. What makes a decent anode seems to make sense as it is a lower potential area that can accept a lot of lithium ions without being damaged (high cycle life). However, what makes a good cathode still isn't as straight forward to me. It seems the ionization energy of the metal oxides are really important towards power density, but I don't really understand why metal oxides are used.
My guess is something like this: Ionizations of metal oxides leave positive metal ions transitions such as $\ce{Ni^2+}$ -> $\ce{Ni^3+}$, $\ce{Cu^2+}$ -> $\ce{Cu^3+}$, and $\ce{Mg^2+}$ -> $\ce{Mg^4+}$ . Lithium is also positively charged so you are creating a lot of potential energy by shoving lithium into these metal ion locations. Since this is very high energy lithium will spontaneously flow out of the matrix if allowed and maintain good stability with the lost lithium due to the ionization of the metals in the oxide. Good anode materials like lithium metal and crystalline silicon can absorb a lot of lithium, but they would not have a high potential energy for discharge making them unsuited for being a cathode material. Is this why metal oxides are used? Why are metal oxides so good at this? What exactly prevents the lithium ions from just flowing to the anode when not under load?


texts: Can rays be considered a type of "element"?

texts:
First of all, I hardly know any chemistry, so let's get that out of the way.

I have been wondering lately, from a "common sense" point of view (owing to my lack of knowledge), that since air cannot be seen and yet is considered as being made up of elements, then what precludes us from considering things like x-rays and radio waves to be elements? What precludes the electromagnetic spectrum from being considered an element? What about light and gravity, or the four fundamental forces?

If someone could kindly elucidate the differences between these categories of "thing", I would highly appreciate it and it would remove much confusion that I have been experiencing lately.


texts: Can the Belousov-Zhabotinsky reaction be simulated with the Brusselator?

texts:
I'm trying to simulate the Belousov-Zhabotinsky reaction mathematically, with a system of ODEs. I know how to do this with the Oregonator and now I'm looking for another model to simulate the BZ-reaction.

The Brusselator model is often mentioned as a model to simulate an oscillating reaction and now I'm looking for a paper/article that uses the Brusselator to simulate the BZ-reaction. But till now, I have not found much, so I'm wondering if it even is possible to simulate th BZ-reaction with the Brusselator?

If it is possible, can you point me to a paper that uses the Brusselator to simulate the Oregonator?

If not, why can't the BZ-reaction be simulated with the Brusselator? And are there alternative models I can use, besides the Oregonator?

Thanks a lot in advance!


texts: Magnetic moments of tetrahedral Cobalt (II) and (III) complexes

texts:
From the spin-only formula we can predict that for tetrahedral cobalt (II) complexes $$m_{eff} = 3.87 \mu_B $$

This ignores orbital angular momentum effects, which result in higher magnetic moments for the tetrahedral halide complexes (Hund's 3rd rule results in spin-orbit coupling "together"). Why do the Co(II) cyanide and Co (III) alkyl complexes have lower magnetic moments than the spin only formula predict ? I have quoted values of 2.15 $\mu_B$ and ~3 $\mu_B$ for these cases.


texts: How do I know with which oxidation numbers I can form a certain kind of compound?

texts:
Take, for istance, phosphorus; it has eight different oxidation numbers, but it can only form two different anhydrides, phosphoric (when the oxidation number is 5) and phosphorous (when it is 3). How do I understand which ones I can use to get anhydrides?
 Or take chlorine, it also has eight oxidation numbers but if I wanted to know the corresponding hydracid, HCl, how'd I know which number to use?

Please forgive me if the question is trivial and written in a poor english, but I'm having trouble with both chemistry and English language classes at present!


texts:
Theoreticly, the width of the spectral line in  AAS (atomic absorbtion spectroscopy) is 10^-5, but in fact there happens an extention of it and it becomes 0.002-0.005. There are some factors which lead to this extention. Most common types of extentions are :

Doppler extention
Pressure extention
Self-absorbance extention.

Does anyone know how to explain in a simple way why do these 3 kinds of extentions take place?

Do these deviations happen all the time in these measurments or are they some deviations that can happen in case the concentration of atoms is to high?


texts: A full verion of the periodic table (For computer game)

texts:
I am looking for a full set of data on every element on the periodic table. (and if possible those only speculated about)

When I say full I mean everything. Electron configurations, Valence electrons, melting point, Atomic mass, Isotopes and what they decay into and all the rest.

Is there such a database anywhere?


texts: Discrepancy when calulating mol weights with ChemSketch and Python RDKit

texts:
I am an IT guy with little knowledge of Chemistry, so please bear with me...
For context: I am working with a system that has a lot of structures, their .mol files and some metadata (like mol weights) in a database. Due to an error, some of the metadata was lost and needs to be recalculated. Since there are a lot of structures, I need to automate this.
Originally, the mol weights were calculated using the Freeware version of ACD ChemSketch. Since I did not find a way to call ChemSketch and have it return the mol weight or otherwise automate ChemSketch itself, I looked at RDKit for Python as an alternative.
In my tests, I noticed that ChemSketch and RDKit produced slightly different results when calculating the mol weights. I used m = Chem.MolFromMolFile('amisalin.mol') to load the file and then MolWt(m) respectively ExactMolWt(m).
Example mol file amisalin.mol:

  -ACD/LAB-

 18 17  0  0  0  0  0  0  0  0  0 V2000
   18.3905   -6.6892    0.0000 C   0  0  0  0  0
   19.4429   -6.0748    0.0000 C   0  0  0  0  0
   18.3905   -8.0661    0.0000 C   0  0  0  0  0
   17.2059   -5.9960    0.0000 C   0  0  0  0  0
   20.5930   -6.7427    0.0000 N   0  0  0  0  0
   19.4429   -4.2757    0.0000 O   0  0  0  0  0
   17.2059   -8.7560    0.0000 C   0  0  0  0  0
   16.0211   -6.6892    0.0000 C   0  0  0  0  0
   21.7398   -6.0748    0.0000 C   0  0  0  0  0
   16.0211   -8.0661    0.0000 C   0  0  0  0  0
   22.5401   -6.5380    0.0000 C   0  0  0  0  0
   14.8742   -8.7309    0.0000 N   0  0  0  0  0
   23.6965   -5.8762    0.0000 N   0  0  0  0  0
   24.8434   -6.5380    0.0000 C   0  0  0  0  0
   23.6965   -4.0709    0.0000 C   0  0  0  0  0
   25.9934   -5.8762    0.0000 C   0  0  0  0  0
   24.8434   -3.4124    0.0000 C   0  0  0  0  0
   21.0845  -12.6663    0.0000 Cl  0  0  0  0  0
  1  2  1  0  2  0  0
  1  3  2  0  1  0  0
  1  4  1  0  1  0  0
  2  5  1  0  2  0  0
  2  6  2  0  2  0  0
  3  7  1  0  1  0  0
  4  8  2  0  1  0  0
  5  9  1  0  2  0  0
  7 10  2  0  1  0  0
  9 11  1  0  2  0  0
 10 12  1  0  2  0  0
 11 13  1  0  2  0  0
 13 14  1  0  2  0  0
 13 15  1  0  2  0  0
 14 16  1  0  2  0  0
 15 17  1  0  2  0  0
  8 10  1  0  1  0  0
M  END

Results:

Average molar weight
Exact molar weight

Chemsketch
271.78628
271.14514

RDKit
271.7919999999999
271.145140004

As you can see, the results are slightly different. Since the input data is identical, I assume this is due to some internal differences when calculating the weights, possibly due to rounding (?).
My question now is: Is the difference negligible? Does anyone know where it comes from? Is one of the results "correct" / more accurate than the other?


texts: Brass - is this corrosion or oxidation and why did it happen?

texts:
I have bought a new brass Y-split water valve which is plain brass but inside is a more polished one, it was packed nicely and I opened it 2 days ago, washed it off with water for some reason, then did a bit of drying with a kitchen towel, I then placed it in a plastic container, however it was more of placing it ON a plastic container as I did not seal it or anything.

Today (2 days after, not even 48 hours are passed) I checked it, and on one of the side the brass had these violet/bluish spots (which I thought are reddish/brown spots at first - but at better lightning they are more of a violet/bluish - my photos really do not show their actual colors). So what are they and why did it happen? This valve splitter is used for water so I don't know why this happened if water was the problem.

I tried to scratch it off with paper towels, and then a toothpick - but it did not work. I did not use anything besides water - and it looked perfectly fine 48 hours ago. Similar thing happened to a water aerator - had a perfect new one I actually checked it, put it on the water tap and ran like 3 liters of water and then I wanted to fix something so I got it out and boom it had these brown - reddish spots, but not this dense and this is not that color.

IF this in case is corrosion, my question would be is it possible for the corrosion to happen this fast only from water? Will the corrosion spread and how bad would it be to be used for a washing machine in terms of a health hazard or machine damage (besides leakage)? Again note that the color is not as dramatic as this and the pictures make it looks much more deeper than it is in real life, whereas it looks like there are stains just atop - although they can't be removed.


texts: Stable oxidation state for Thallium and indium

texts:
The first Ionisation Enthalpy for Thallium is ~ 590 KJ/mol whereas that for Indium is ~ 558 kJ/mol. But why is +1 oxidation state more stable for Tlthan In?
What are the other criteria that explain the stable +1 oxidation state of Thallium?


texts: Is Kp and Kc only effected by temperature?

texts:
Are Kp and Kc only effected by temperature?

So in exothermic and endothermic equilibrium reactions you are increasing or decreasing temperature, which will effect which side is favourable.

But then so does pressure if one side has fewer molecules?


texts: Role of solvents in ozonolysis and oz0nolysis of alkynes with water

texts:
My text book says that when an ozonide (formed from an alkene) is treated with $\ce{Zn/CH3COOH}$, it cleaves to give carbonyl Compounds.

1) Does $\ce{ Zn/CH3COOH}$ mean Zinc in acetic acid (or) zinc or acetic acid. I at first thought that it should be zinc in acetic acid, but then I found a separate mechanism for acetic acid alone, (given below) which made me confused. So, which one is it?

2) If the above mechanism is correct, then why doesn't the oxygen-oxygen bond (being unstable and weak) cleave in the step I've encircled?


texts: Reaction of Grignard reagent with primary amines

texts: What does the reaction $\ce{CH3CH2NH2 + CH3MgBr ->}$ form?  Does it form a secondary amine or a tertiary amine or an alcohol? I can't find what a Grignard reagent does to a primary amine.


texts: Why are there 2 equivalents of Ca in an example stated in Wikipedia?

texts:
Applying what's been said in the Wikipedia page for equivalents, if $1\ \mathrm{mol}$ of $\ce{NaCl}$ and $1\ \mathrm{mol}$ of $\ce{CaCl2}$ are dissolved in a solution, there is $\rm1~eq~Na,~2~eq~Ca$, and $\rm3~eq~Cl$ in that solution.

Is this a misstatement in Wikipedia?


texts: Do alkenes have priority over alkynes in R/S naming?

texts:
I am studying for an upcoming exam and I came upon a confusing question for the drawing of the molecule (3R)-hex-1-en-5-yn-3-ol.

Why is the stereocenter (3-carbon) R? Shouldn't it be S? After looking at it, I see that the priority is OH > alkyne > alkene. I'm really confused.


texts: How are the LCAO ansatz and Slater determinant ansatz for the wavefunction connected?

texts:
Say we have a system of 2 electrons, an ansatz for the wavefunction is then a Slater determinant consisting of two orbitals.
$$
\left|\Psi_{Slater}\right>= \frac{1}{\sqrt{2!}}\left(\left|\phi_1\phi_2\right>-\left|\phi_2\phi_1\right>\right)
$$

How is this related to the basis expansion ansatz:
$$
\left|\Psi\right>= \sum_i c_i \left|\phi_i\right>
$$

The basis expansion formula would give me a function of 1 coordinate x_1 if i projected it on the position space, while the slater determinant ansatz would give me a function of two coordinates x_1, x_2. x_i stands for a set of x,y,z
coordinates. Spin is neglected in this example.
I understand that for the basis set expansion in an orthonormal basis, one can obtain the coefficients by the inner product
$$
\left<\phi_i|\Psi \right>=c_i
$$

but how can i use this on a slater determinant ? I only understand how this works if everything relies on one coordinate x_i, then i can calculate this:
$$
\left<\phi_i|\Psi \right>=\int\phi_i(x)\Psi(x)dx=c_i
$$

But how does this work if the wavefunction is multidimensional like the slater determinant wavefunction ?
$$
\left<\phi_i|\Psi_{Slater} \right>=\int\phi_i(x_1)\Psi_{Slater}(x_1,x_2)dx= c_i(x_2)?
$$
This expression makes no sense, since the remaining object would still be a function of $$x_2$$

To my knowledge only basis functions of one coordinate are used in calculations, like 3D Gaussians. Assuming that i have a wavefunction given in slater determinant form, how would i find the coefficients of the basis functions ?

I am afraid i am mixing up things that don't belong together, clarifications would be welcome.


texts: Direction of arrows in electrocyclic reactions

texts:
We recently started learning about pericyclic reactions and this is a step from a mechanism I'm working on for an assignment. I believe that the arrows on the right are better than the arrows on the left because if I throw in some charges instead of arrows, the outcome I get on the right is somewhat more "stable?" for the reasons stated on the picture. Am I correct in my assumption?
 On the overall reaction,  it's the 6 to 7 step that I'm interested in.


texts:
I'm currently removing rust on some bike parts so decided to use electrolysis. It's working fine, but the solution has turned a deep/dark blue whilst in most online videos it turns orange with the rust. My sacrificial anodes aren't stainless or chromed, and I dont believe they're galvanized either.

Is the blue colour any cause for concern (am I making anything toxic accidentally)?


texts: Does a first order reaction really get completed only at infinity?

texts:
For a $1^{\text{st}}$ order reaction $ A \rightarrow B$, the corresponding rate law is: $$\text{rate} = k[A]^{1}$$ and the integrated rate law for this is $$ \ln \left(\frac{A}{A-x}\right) = kt$$

Going by this equation, every first-order reaction must get completed only at infinity. Is this true? If not, then what is the correct explanation?


texts:
I was wondering about $ \ce{CaCl2} $ hydrolysis.
The most primitive answer would have been:
$ \ce{Ca(OH)2} $ does not dilute that great, therefore it is not strong enough to have the $ \ce{Ca^2+} $s not hydrolise. Thus:
$$
\ce{Ca^2+ + H2O <<=> CaOH^+ + H+}
$$
Yet, as we can see in this answer - $ \mathrm{pK_B^{II}} $ for $ \ce{Ca(OH)2} $ is $ 1.4 $, which is not bad. Therefore, some reckon the diluted part of $ \ce{Ca(OH)2} $ to be a pretty strong base, making hydrolysis impossible. To make things worse, the cation hydrolysis is known to be harder to trace rather than anion hydrolysis.
Still, I have come across some articles on $ \ce{CaCl2} $ hydrolysis (like this one - a top Google search line; yet, this one first shows that $ \mathrm{\Delta G_{900^oC}} $ is $ \mathrm{90.951 >  0} $).
So, is it safe to say that at $ \mathrm{\approx 25^oC} $ $\ce{CaCl2}$ does not undergo hydrolysis?


texts: Determination of (R) and (S) configurations from a Haworth projection

texts:
Short version of question : How do I know which groups are equivalent to "out of and into the page (like in the Fisher projection)" for the Haworth projection (so that I can send the lowest priority group to the "back")?

Details:

I am comfortable enough finding R and S configuration of Fischer projections, but am unsure which groups are coming in or going out of the plane of the page in a Haworth display.

For example:

Figure 1

Taking carbon $3$ for example, the priorities are as shown below in blue:

Figure 2

By definition, horizontal groups are out of the page (i.e. towards us) and vertical groups are into the page, the lowest priority group (hydrogen) is out of the page. If hydrogen was into the page, carbon $3$ would have a clockwise R configuration, but as hydrogen is drawn out of the page, carbon 3 has the opposite, hence an  anticlockwise S configuration.

If I now took carbon 3 in the Haworth for the structure above, I am assuming it is still an S configuration as the groups are still in the same position around the carbon 3 atom, relative to the other groups.

Update: After seeing the following image (annotated with numbered carbons from this source) I am not so sure about that anymore as carbon 4 has different configurations in the Fischer vs the Chair and Haworth.

Figure 3

But how would I determine the R and S configuration of carbon 3 without going back to the Fischer projection?

Mainly, how do I know which groups are equivalent to "out of and into the page (like in the Fisher projection)" for the Haworth projection (so that I can send the lowest priority group to the "back")?

I would think carbon 4 is "into the page" as it is further away from our point of view (which matches the Fischer projection, as it is drawn vertically there).

Based off this, carbon 2 would also be into the page (as its the same as Carbon 4 in the Fischer projection). Hence, the $\ce{OH}$ and $\ce{H}$ would be out of the page.

The priorities would be as follow:

Figure 4

If $\ce{H}$ was into the page, as draw it would be R, but as $\ce{H}$ is into the page, its the opposite and hence carbon 3 is an S

So I arrive at the same answer, but mainly due to comparing the Haworth off of the Fischer projection. How would I judge what was in and out of the page without the Fischer projection and only the Haworth?


texts: Ortho-effect in substituted aromatic acids and bases

texts:
When comparing o,m,p-toluidine basicities, the ortho effect is believed to explain why o-toluidine is weaker. But when comparing o,m,p-toluic acid basicities, the ortho effect is stated as a reason why o-toluic acid is stronger acid. I was told that the ortho effect is a phenomenon in which an ortho- group causes steric hindrance, forcing the $\ce{-COOH}$, $\ce{-NH2}$ or some other bulky group to move out of the plane, inhibiting resonance. Then, if the ortho effect inhibits resonance, why is o-toluic acid the strongest and o-toluidine the weakest?

Where am I going wrong in my understanding of the ortho effect?


texts: Why is ethanol distilled off before adding water in the first step of a malonic synthesis?

texts: I am doing a malonic synthesis shown below, and I wonder why I should distill ethanol off before adding water in the first step of the reaction (First I add absolute ethanol and solid sodium).


texts:
Recently in the Chemistry.SE chatroom a user posted this to celebrate the New Year:

Can Ca and K exist as an ionic compound? If not, why is it impossible?

  Ca with atomic number 20, K 19
  so 2019 ->Happy New Year->2020


texts: Aflatoxin versus Benzene, permissible levels

texts:
Alfatoxin and benzene are carconogenic, and this is the major concern for low, chronic doses. They are regulated to the few parts per billion level in food. However, according to http://toxnet.nlm.nih.gov/cpdb/pdfs/ChemicalTable.pdf,
aflatoxin is three to five orders of magnitude more carcinogenic, as evident from the lower doses needed to induce tumors in rodents.

Why are the permissible thresholds similar?


texts: Why are triple covalent carbon to carbon bonds drawn linearly in skeletal structure?

texts:
In the link see that cyclic C-C structure with a triple covalent bond is drawn with an angle, probably the only way to draw it but why is it drawn linearly in non-cyclic and not like single or double bond? I am wondering about the reason for this not that its a convention.

Alkyne Wikipedia


texts:
Why is it said that the presence of a carbon with 4 different groups is necessary for it to exist as an enantiomeric form?

Lets take 2-fluoropropane for example.

When I draw the structure of it in such a way so that the 2 CH3 groups are adjacent to each other (on paper ) and take its mirror image I see that I got a mirror image which is not superimposable on the original structure. My teacher told me I am only allowed to rotate it in the plane of the paper and only by 180° without lifting it out.

This seems to tell me that they are a pair of enantiomers( non superimposable mirror images).

On the other hand when I draw the structure such that the 2 CH3 groups are on opposite sides of the central carbon and then take a mirror image of it , rotate it by 180° in the plane of the paper I get the original structure.
This tells me that they are not stereoisomers.

Also where is the mirror supposed to be placed - up down left right? Any convention (here I have placed the mirror on the right)?


texts: Balancing the equation for the preparation of dichromate from chromite ore

texts:
$\ce{FeCr_2O4 + Na2CO3 + O2 -> Na2CrO4 + Fe2O3 + CO2}$

I have tried balancing it by writing the reduction and oxidation half equations viz. :

$\ce{2Fe^{+II}Cr_2^{+III}O4 -> 4Na2Cr^{+VI}O4 + Fe2^{+III}O3 + 14e^-}$

And:

$\ce{3O2^{0} + 12 e^- -> 2Fe2O3^{-II} } $

Then I multiplied the first equation by 6 and second by 7 and added them and though the electrons got cancelled, it turned out to be really hard to make any progress.

Could someone please provide the technique for balancing such an equation?


texts:
I keep hearing about this product known as triclosan, and that it is used in sanitizing soap. And I also heard that it is harmful, and causes some sort of muscle problems.

However some people aren't affected by it. Why is this, and should I
 be worried about washing my hands?


texts: Use of powder of kernel of tamarind seeds for water purification

texts:
In the chapter Environmental Chemistry in our textbook it's given that Powder of Kernel of Tamarind seeds can be used for water treatment as a substitute for alum.
But if I understand correctly, alum ionizes in water and these ions neutralize the electrical double layer surrounding colloidal particles. How does a substance like 'Powder of Kernel of Tamarind seeds' produce the same effect?


texts: R/S configuration of bridging carbon in bicyclic system

texts:
I am trying to figure out the R and S configuration of bridging carbons in bicyclic systems.
In the image, there are two bicyclic systems and depending on the position of the Br substituent, the R or S configuration of the bridging carbons change. How is the configuration actually determined? I don't understand how the prioritization works in this case, as two substituents are similar. Thus, the reason must be the adjacent stereocenter... But I am not able explain it properly.


texts:
I carry around a toiletries bag. I put my toothbrush there right after brushing in a restaurant or some public area.

These strangely similar articles(1, 2) suggest toothbrushes have to be aired. Why exactly? What harm does the wetness on the bristles cause?


texts: Thermodynamics in Solution (solvation) from quantum chemistry

texts:
The gist of the question is "how do I get a heat of formation in solution" - but let me give it some context to be more specific.

I am interested in calculating the thermodynamic values of molecules in solution. Due to the number of jobs, time etc. I have to use DFT methods. These are not as accurate as for example CCSD related methods but still provide good answers in reasonable timeframes (plus I'm checking up on estimated values, so I don't immediately need the highest acutacy).

As atomisations are hard to calculate with DFT methods (see a book by Cramer & comment on the ORCA forum), isodesmic reactions offer a better option.
So far so good. This allows me to use literature values for reference compounds to calculate the heat of formation of a species.

Now I need the heat of formation of the species in the liquid phase.
I can repeat my quantum chemistry calculations with a solvation model and again obtain values - however I now lack the reference compounds.
Based on my understanding of chemistry (see textbook by Cramer) I can relate the Gibbs free energy of the gas phase molecule with the solvated molecule.
So using the following:

$G_{liq} = G_{gas} + G_{sol}$
$\delta G = \delta H_f - \delta S ~T_{LO}$

I can work out the liquid phase heat of formation of the molecule.
(Please correct me if I am wrong.)

Now here is a little problem:
For organic molecules, there can be multiple local minima - but only one absolute total minimum.

The total minimum can correspond to a different structure in the gas and liquid phase, so do I compare structures and consider them or do I use the total minimum in both cases, I.e the lowest energy structure to calculate my thermodynamic data?

Reference:
Essentials of Computational Chemistry: Theories and Models, 2nd
Edition Christopher J. Cramer
http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0470091827.html


texts: Why increase in enthalpy leads to increase in entropy?

texts:
Given statement: Enthalpy of adsorption is the strength at which molecule (say $\ce{H2}$) is bound to the adsorbent (say some metal center). For a free $\ce{H2}$ molecule, the entropy contribution is from translational, rotational and vibrational motion. After the adsorption, the translational and rotational motions will not contribute to the entropy change $\mathrm{\Delta S}$. Thus the only contribution to $\mathrm{\Delta S}$ is from the vibrational motion of $\ce{H2}$ which will decrease for increase in adsorption strength.
As per the given statement, increase in enthalpy should decrease the entropy. However, Enthalpy-Entropy correlation states that increase in enthalpy leads to increase in entropy. How this is true?


texts:
Is dextrose an optical isomer of glucose?

If a microorganism metabolises glucose, would it also be capable of metabolising dextrose? Do both 'fit' into the same enzyme that binds to glucose?


texts: How would using different salts in a salt bridge effect the voltage generated by a voltaic cell?

texts:
If I use a range of different nitrate solutions (e.g. calcium nitrate, iron nitrate) for the salt bridge in a voltaic cell, what effect would it have on the flow of ions in the voltaic cells?

Will the different properties of the salts such as ionic radius effect the voltage generated by the voltaic cell?

If a certain property would most likely have an effect, what would it be and why?

(Both the cathode and the anode are kept constant with copper in copper nitrate solution and zinc in zinc nitrate solution)


texts: Would the same equilibrium concentration of carbon dioxide, carbon monoxide and oxygen always result for a given initial atomic carbon fraction?

texts:
Chemistry SE Question: Starting with a gas mixture of some combination of gases containing carbon and oxygen with a total carbon atomic fraction $f$, would it always reach the same equilibrium proportions of $\ce{CO2 + O2 + CO}$?

For example if I had an equal number of $\ce{CO2}$ and $\ce{O2}$ molecules then $f=0.2$, but so would two molecules of $\ce{CO2}$ for every three molecules of $\ce{O2}$. If I started with either mixture in this example, would I end up with the same equilibrium mixture of $\ce{CO2}$ and $\ce{CO}$ and $\ce{O2}$?

Simplifying assumptions: Assume $\pu{273K}$ and $\pu{610Pa}$ if necessary, the answer may be as simple as "yes it would" or "no it wouldn't, because...", a supply of ionizing radiation from space (hard UV and energetic cosmic ray particles) and a billion years, and ignore transmutation of elements by those particles.

Background and motivation is from my Space Exploration SE question Are Mars' atmospheric CO₂, O₂ and CO in equilibrium? Are sunlight or chemical reactions involved?, which begins:

  According to the NASA JPL video linked below the top five gases comprising the martian atmosphere include $\ce{CO₂, O₂}$ and $\ce{CO}$. Do the proportions reflect some chemical equilibrium? Are sunlight or chemical reactions involved in maintaining these proportions?

Component     Fraction
   CO2          95.9%
   Ar            2.0%
   N2            1.9%
   O2            0.14%
   CO            0.06%

  The NASA JPL video Crazy Engineering: Making Oxygen on Mars with MOXIE is linked in How many square meters of solar panel to power a MOXIE-like oxygen source per person?.


texts: Why is the difference between the melting point and boiling point large for some compounds, and small for others?

texts:
I was looking at a list of melting and boiling points of various compounds and I realised some had very large differences while some have very less differences between their melting and boiling points.

Example:

for cyanogen, boiling point is -21.2°C while melting point: -27.9°C
for propane, boiling point: -42 °C while the melting point:  -144°C

Why does this happen?


texts: Why are the given compounds in a homologous series?

texts:
Why are the given compounds in one homologous series?

$$\ce{CH3-OH}$$
  $$\ce{CH3-CH2-OH}$$
  $$\ce{CH3-CH2-CH2-OH}$$
  $$\ce{CH3-CH2-CH2-CH2-OH}$$

I know that homologous series can be represented by a common general formula and have the same chain length. But I could not answer this question. Can anyone help me?


texts: How to write the Nernst Equation for this reaction?

texts:
I am required to write the Nernst equation for the following reaction:

$\ce{O_2 + 4H^+ + 4e^- -> 2H_2O}$

Clearly, here $\ce{O_2}$ is getting reduced from an oxidation number of zero to an oxidation number of $\mathrm{-2}$ in the water molecule.
Usually, the examples of chemical reactions provided in the textbooks(at least in high school textbooks) for writing Nernst equations are of the form: $$\ce{M^{n+}(aq) + ne^- -> M(s)}$$ and the Nernst equation for this electrode reaction is given as: $$E_\ce{(M^{n+}/M)} = E^\circ _\ce{(M^{n+}/M)} - \frac{RT}{nF}\mathrm{ln}\frac{1}{[\ce{M^{n+}}]}$$
But here, in this case, the oxidation state for the $\ce{H^+}$ remains the same on both side of the reaction, rather the oxygen gas gets reduced. And this is what is confusing me.
The solution provided states that the equation should be: $$E = E^\circ+\frac{0.059}{4}\mathrm{log}[\ce{H^+}]^4 \cdot P_\ce{O_2}$$
I specifically didn't understand the reasoning behind writing the part that comes after log.
Please explain.


texts: Graph representation of polymer nanocomposites

texts: Graph theory has been used as a means of representing molecules for decades. For a single molecule, a graph representation assigns a vertex for every atom in the molecule and the covalent bonds are represented using edges of the graph, which connect the pairs of vertices. I was wondering if there are established representation for multi-component materials as a single graph, in particular polymer nanocomposites?


texts:
This is an extremely basic question about biochemistry from someone who doesn't know much about organic chemistry. I'm aware of how organisms store energy ATP and release it by dephosphorylating it into ADP. My question is about the role that the adenosine part of the ATP molecule plays in this process.

Naively, it seems as if the triphosphate group could be attached to any old thing, and you'd get the same energy by dephosphorylating it. But as far as I'm aware, it's only ATP that's used for this purpose in biology, and not any other triphosphate. Why is this? Is the fact that the triphosphate is attached to an adenosine just a "frozen accident" like the genetic code, or does it play an important role in the phosphorylation/dephosphorylation reactions themselves?


texts: What happens to the solute when a solution freezes?

texts: I came across a situation in which my chemistry textbook gives phase diagram of a pure solvent and a solution with the same solvent.I am considering 2 different , say beakers, one containing some amount of pure solvent , and the other contains a solution formed by a non volatile solute and the same amount of solvent. In this, the author has shown the part of the graph corresponding to solid solvent , and solid form of solution to be identical. It's natural for me to think that a solid obtained by freezing a solution would be different from that obtained by freezing a pure solvent. So they must not have identical graphs. Is my argument correct ? Or is it like this- when the solution is frozen , since the solvent molecules are brought together for making a solid, we simply don't have solvent molecules to solvate  our solute, and the solid is more or like a frozen pure* solvent with solute particles trapped in it?


texts: Why does raising the temperature affect the mass of dissolved solute?

texts:
Consider a solution of $\ce{KOH}$ which is in equilibrium with undissolved $\ce{KOH}$ at $25\ \mathrm{^\circ C}$.
After raising the temperature to $50\ \mathrm{^\circ C}$, the mass of undissolved $\ce{KOH}$ decreases. Why is this?


texts: Which factors best account for the increase in boiling point?

texts:
The boiling points of $\ce{CH3COCH3}$, $\ce{CH3COC2H5}$, and  $\ce{CH3COC3H7}$ are $56˚C$,
  $80 ˚C$, and $102 ˚C$, respectively.  What factor(s) best account(s) for this?

I believe london dispersion forces is one of them. Is dipole-dipole interactions another one? It seems to me that there are dipole-dipole interactions since none of the structures of symmetrical, so can they account for this increase in boiling point?


texts:
Whilst reading the book, So you want to go to Oxbridge (Third Edition), I noticed that it states that a past question given during an interview for the place on the undergraduate chemistry course (M.Chem) was:

  What happens to the mobility of Group 1 elements going down the
  periodic table?

I do not understand the question. And so, I would both like to understand the question and know and understand its answer.

Preemptively, Thank you


texts: Energy level of molecular orbitals in heteronuclear diatomic compounds

texts:
I have been studying the molecular orbital theorem. I read that the energy levels for the $\ce{p}$ orbitals in the first series of $\ce{p}$ block molecules are something to the tune of $$\pi_x=\pi_y<\sigma_z<\pi_x^*=\pi_y^*<\sigma_z^*$$

except for $\ce{O2 and F2}$, which have
$$\sigma_z<\pi_x=\pi_y<\pi_x^*=\pi_y^*<\sigma_z^*$$

But it got me thinking: what order would the orbitals take in a compound such as $\ce{CO, NO}$?

(Also, out of curiosity, what about $\ce{p-p}$ bonds in higher series of the $\ce{p}$ block? Does $\ce{Cl2}$ have the same order as $\ce{O2}$?)

My guess was that since in heteronuclear orbitals more electronegative elements have lower energy orbitals, compounded with the fact that the $\sigma$ orbitals it forms tend to be lower energy, it should follow the latter’s order.


texts: Bisulfate vs Bisulfite to neutralize off gassing in paint

texts:
I need to neutralize the off gassing in wall paint that contains one or more of the antimicrobial compounds of  isothiazolinone, chloromethylisothiazolinone, methylisothiazolinone, benzisothiazolinone, or octylisothiazolinone.

I applied and used sodium bisulfate rather than sodium bisulfite. Do I need to now rinse it off and find the sodium bisulfite or will the sodium bisulfate work?

Link to study using sodium bisulfite.


texts:
I just want to know how to electrons travel from one end to the other.

The concept I have in my mind is that the ions functions as "buses" for the electrons then send them to the other side, but doesn't that make them neutral molecules? (in which case they wouldn't be attracted to the + side.)


texts: What is the formula for evaporation rate of water?

texts:
I did my own research, and according to The Engineering Toolbox,the formula for the evaporation rate of water is as follows:

$g_\mathrm h = \Theta A (x_\mathrm s - x)$

$g_\mathrm h$ = amount of evaporated water per hour ($\mathrm{kg/h}$)

$\Theta = (25 + 19 v)$ = evaporation coefficient ($\mathrm{kg/(m^2\ h)}$)

$v$ = velocity of air above the water surface ($\mathrm{m/s}$)

$A$ = water surface area ($\mathrm{m^2}$)

$x_\mathrm s$ = humidity ratio in saturated air at the same temperature as the water surface ($\mathrm{kg/kg}$)  ($\mathrm{kg}$ $\ce{H2O}$ in $\mathrm{kg}$ dry air)

$x$ = humidity ratio in the air ($\mathrm{kg/kg}$) ($\mathrm{kg}$ $\ce{H2O}$ in $\mathrm{kg}$ dry air)

However, later I realized that something is wrong with the formula. There is no variable for water temperature.

The formula for humidity ratio in the air is:

$$x = 0.62198 p_\mathrm w/(p_\mathrm a - p_\mathrm w)$$

$p_\mathrm w$ = partial pressure of water vapor in moist air (Pa, psi)

  $p_\mathrm a$ = atmospheric pressure of moist air (Pa, psi)

The formula for humidity ratio in saturated air is the same, except partial pressure of water vapor in moist air is replaced with saturation pressure of water vapor in moist air.

And the formula for water vapor saturation/partial pressure is:

$$p_\mathrm{ws} = \mathrm e^{\frac{77.3450 + 0.0057 T - 7235 / T}{T\cdot8.2}}$$

$$p_\mathrm w = p_\mathrm {ws} \cdot HU$$

$p_\mathrm{ws}$ = water vapor saturation pressure (Pa)

$T$ = dry bulb temperature of the moist air (K)

$HU$ = humidity ratio (%)

So, according to this website, temperature-wise the formula is determined solely by the air temperature without considering the water temperature. Is it because the formula assumes the equivalence of the two temperatures for simplification or because I'm missing a variable? I searched for other methods, but so far no website is as comprehensive as this one, and I don't want to re-program everything again.

This is a different question from the existing ones. I've read many of them and the answers are not specific enough for my situation. Here I need to know how the temperature of the water plays a role in the formula for the rate of evaporation of water.


texts: Why is formyl chloride unstable while higher acyl chlorides are stable?

texts:
Source: Paula Bruice Ed. 2017 Pg.877

From this excerpt, we infer that formyl chloride is unstable.
But how does that affect the reaction in any way? Is it just mentioned as a point to note or does it have an effect on the reaction. And if acetyl chloride is unstable why is acyl chloride stable?

Also note that I do realise that this is a duplicate of
Stability of formyl chloride

But we’ve not used water in Gatterman Koch reaction as reasoned by @SimpliFire in the thread. So how does it remain unstable even when water is not involved.


texts: Why can unsymmetrical tert-butyl ethers be prepared by dehydration of the constituent alcohols?

texts: Practice problem 11.11 what stops R-O-R from forming at the same rate as the desired product?


texts: Work done by one mole of gas during isobaric and isothermal expansion

texts:
If $100\ \mathrm{mol}$ of $\ce{H2O2}$ decomposes at $1\ \mathrm{bar}$ and $300\ \mathrm K$, the work done ($\mathrm{kJ}$) by one mole of $\ce{O2(g)}$ as it expands against $1\ \mathrm{bar}$ pressure is:
$$\ce{2H2O2(l) <=>2H2O(l) +O2(g)}$$

My attempt to solve the problem:
Since $2\ \mathrm{mol}$ of $\ce{H2O2}$ decomposes to give $1\ \mathrm{mol}$ of $\ce{O2}$, so $100\ \mathrm{mol}$ of $\ce{H2O2}$ will give $50\ \mathrm{mol}$ of $\ce{O2}$.
Now, The work done by $50\ \mathrm{mol}$ of $\ce{O2}$ as it expands is,
$$w_{\ce{O2}}=-w_\text{surr}=\int{p_\text{ext}\,\mathrm dV}=p_\text{ext}\,\Delta V=(\Delta n_\text{gas})RT=50\times8.3\times300\times10^{-3}\ \mathrm{kJ}=124.5\ \mathrm{kJ}$$
$124.5\ \mathrm{kJ}$ is in fact the answer given but we are asked to find work done by one mole of $\ce{O2}$.
Shouldn't the answer be $w={124.5\over50}\ \mathrm{kJ\ mol^{-1}}=2.49\ \mathrm{kJ\ mol^{-1}}$?
If $50\ \mathrm{moles}$ of gas expanded to a specific volume, say $V$, then $1\ \mathrm{mole}$ of gas should expand to ${V\over50}$. Then according to me work done by $1\ \mathrm{mole}$ of gas should be ${1\over50}$ of work done by $50\ \mathrm{moles}$ of gas. Does work add up like extensive properties of system?
Reference: This question appeared in JEE Main entrance examination held in India in 2016, the official answers and question papers are not publicly available, all I can find is this pdf https://www.resonance.ac.in/answer-key-solutions/JEE-Main/2016/papers/jee-main-2016-online-CBT-paper-Dt-10-04-2016.pdf#page=19 (Question no. 20 page 19) and the answers (also pdf) https://www.resonance.ac.in/answer-key-solutions/JEE-Main/2016/answer-key/jee-main-2016-online-CBT-solution-Chemistry-10-04-2016.pdf#page=7 (Question 20 Page 7)
$2.49\ \mathrm{kJ\ mol^{-1}}$ as calculated by me doesn't seem to be in the options at all.


texts: Why are ethers treated as substituents and not as functional groups in IUPAC nomenclature?

texts:
Why are ethers not considered as functional groups in IUPAC nomenclature?

Let us consider the following example:

Image source

The PIN for this compound is 2-ethoxy-1,1-dimethylcyclohexane. And we get this by first point of difference as ether is also considered as a substituent here.
But ethers do confer specific properties to the compound. They are studied as a separate functional group. Yet they aren’t given the preference in nomenclature in the absence of any other functional group too. Why is this so? Is it just a convention or is there a reason behind it?

PS: I checked this similar question on our site but it doesn’t answer my question as to why ethers aren’t functional groups when it comes to naming.


texts: How to convert sodium aluminate back to sodium hydroxide?

texts:
I had dissolved a bunch of aluminium foil in an aqeous solution of sodium hydroxide. The resulting solution consists mainly of sodium aluminate with very little excess sodium hydroxide.
What I want to do is convert this back to sodium hydroxide. I am thinking electrolysis should do the trick. But, I am not completely sure if this is right. If it is, what kind of electrodes should I use? If not, why not? (What will be the product?)
Thank you for your time.


texts: I have a small amount of a powder that is roughly 100 microns but I need to get it down to less than 10 microns. It is a small amount so I can't send it to any factory specializing in that as far as I know. In your opinion, what's the best way (cheapest) way to decrease the particle size (so far I've only been able to find coffeee grinders but it is unlikely they'll be able to get the particle size down to 10 microns) to less than 10 microns?


texts: Why does ozone have such a large solubility in water?

texts: At $25~\mathrm{^\circ C}$, the solubility of ozone is $109~\mathrm{mg~L^{-1}}$. This is $13$ times higher than the solubility of diatomic oxygen. What causes this?


texts: Coefficients in K2SO4 electrolysis scheme (textbook)

texts:
From a textbook, a scheme of $\ce{K2SO4}$ electrolysis:

I don't understand how the two equations with the coefficients 2 before the water combine into the equation with the coefficient 6. Would not the coefficient before $\ce{H2}$ be 1.5 then?

The text is

  When a salt consisting of an active metal and an oxygen-containing acid moiety is subjected to electrolysis, both cathode and anode participate in the electrolytic dissolution of water.


texts: Does Mie Scattering occur in Liquid or is Rayleigh scattering?

texts:
Rayleigh scattering occurs when the dimensions of the scatter is much smaller than the wavelength of the incident electromagnetic radiation.

Mie scattering occurs when the dimensions of the scattered is much larger than the wavelength of the incident electromagnetic radiation. An example is when light is scattered by small water droplets in clouds.

So does Rayleigh or Mie scattering occur in liquid or bulk water?

It seems the answer is Mie scattering. But in Raman spectrometry. The incident light say 532nm is rayleigh backscattered in liquid. This is why the equipment needs to have notch filter, etc. So why does Rayleigh scattering (?) occur in liquid/bulk water when the particles are much larger than the wavelength of light? Or is it Mie Scattering that the raman device is filtering in the incident light backscattered?


texts: Molar concentration of water and pKa value

texts:
By defintion, $\mathrm pK_\mathrm a$ value is defined as
$$\mathrm pK_\mathrm a = -\lg ([\ce{H2O}] K_\mathrm{eq})$$

Consider the reaction:
$$\ce{HCl + H2O <=> H3O+ + Cl-}$$

The Eq constant of $\ce{HCl}$ is defined as

$$K_\mathrm{eq} = \frac{[\ce{H3O+}][\ce{Cl-}]}{[\ce{H2O}][\ce{HCl}]}$$

Why is molar concentration of water fixed at 55.5? Wouldn't it depend on the extent of ionization?


texts: Comparing basic strength of phosphorus trichloride and phosphorus trifluoride

texts:
I need to compare the Lewis basic strength of trihalides of phosphorus
My thoughts :
Since fluorine is more electronegative, the percentage of $\mathrm s$-character in $\ce{P-F}$ bonds will be lower, which will in turn increase the percentage $\mathrm s$-character of the orbital which contains the lone pair of phosphorus atom .
So the lone pair will be closer to the nucleus and so its donation will be more difficult, and thus I came to the conclusion that the order should be
$$\ce{PF3}<\ce{PCl3}<\ce{PBr3}<\ce{PI3}$$
But I have read that $\ce{PF3}$ behaves as a better ligand in coordinate compounds.
Also, I have seen different orders at different places.
Could someone help me figure out the correct order and also the actual reason for that order, and also about whether lewis basic strength and ligand strength go parallel to each other or whether there can be discrepancies in order?


texts: Molecular formula for 4-methyl-1-pentanol?

texts:
According to Wikipedia 4-methyl-1-pentanol is $\ce{C_6H_{14}O}$.

But here is what I got, which is slightly different.

Methyl = Think of methyl group, which is $\ce{CH_3}$.

Pentanol = Penta means we have 5 carbons, -ane ending means we have $2n+2$ hydrogens, i.e. 12 hydrogens and -ol ending means we have a hydroxyl group $\ce{-OH}$.

So the molecular formula that I arrived at is: $\ce{CH_3C_5H_{12}O}$ = $\ce{C_6H_{15}O}$.

How did I end up with an extra hydrogen compared to Wikipedia answer?


texts: Will aluminum continue to corrode after its surface is oxidized?

texts: After doing some reading, it is common to read that aluminum is corroded by oxygen, but that the thin layer of aluminum oxide protects the internal metal from further damage. How much does this layer of aluminum oxide protect the underlying layers? Does it completely seal off the aluminum or is there still a slow degradation compared to a metal like iron?


texts: Why is there a discrepancy among sources on the atomic radius of some elements?

texts:
My book says the atomic radius of gallium is less than that of aluminium, but I found out different atomic sizes on different sites.

For example, this says gallium is 136 pm and aluminium is 118 pm, but Wikipedia says Ga is 130 pm, Al is 125 pm.

Both of them give different atomic radii but are consistent in ordering: both sites say Ga is larger than Al. What is correct?

My book says atomic size of Cr, Mn, Fe is about 117 pm and Zn is 125 pm; these again differ from the values give in the above websites. Which source provides correct values of the atomic radii?


texts: In spectroscopy, is it possible for the sample to be excited multiple times?

texts:
The context of my question is rotational spectroscopy (using microwave radiation), where there is the $J = \pm 1$ selection rule. The way I understand spectroscopy is that the sample is irradiated with a range of frequencies. Is it possible, during the irradiation of the sample (say CO), for the molecule to be excited by 2 levels by 2 successive photons of the appropriate frequencies?

Now this does not affect the locations of the peaks per se, because the relaxation of course has to happen one level at a time. I am specifically wondering about the distribution of peaks, which is supposed to follow the Boltzmann distribution. Let us say, for example, we have a sample at absolute zero, where all the molecules are at the ground state $J = 0$. Is it possible for a molecule to be excited twice (or more), leading to the rotational spectrum showing more than one peak?

Thank you in advance.


texts: Comparing the basicity of aniline and ortho anisidine

texts:
In  my worksheet there is a question that asks for the comparison of basicities of the three anisidine isomers and aniline:

After my analysis using:

$\text{Basicity} \propto \text{+M effect (except for meta annisidine)} \propto \dfrac{1}{\text{-I effect}}$,

I could make the following conclusions:

m-anisidine should be the least basic
p-anisidine should be more basic than aniline.

But the main problem is comparing the basicity of aniline and o-anisidine and comparing them with p-anisidine. I doubt the presence of ortho effect in ortho isomer after seeing the ball and stick model which makes the interaction of lone pair of nitrogen with hydrogen atoms of $\ce{-OCH3}$ improbable.

The answer given is:

   p-anisidine> aniline > o-anisidine > m-anisidine (I have verified it with $pKa$ values from PubChem)


texts: Synthesis of Pseudopelletierine, Mannich reaction base catalysed

texts:
The synthesis of Pseudopelletierine starts from glutardialdehyde, which reacts with methylamine and acetonedicarboxylic acid in a two-fold Mannich reaction.

This is the reaction:

I need to write the mechanism for this reaction. It needs to be under basic conditions also.

.

MY ANSWER SO FAR:

There will be a Mannich reaction followed by a second intramolecular Mannich reaction in order to form a ring by joining al three reagents together. Finally there will be a decarboxylation to remove the carboxylic acid groups.

This is the mechanism I have done:

Is this right? Any help would be appreciated.


texts: I know that salt dissolving in water is driven mostly by entropy. However, at lower temperatures, entropy is less of a factor in controlling reactions. Is there a temperature where salt doesn't dissolve in water?


texts: Using concentrated sulfuric or nitric acid during titration of permanganate with oxalic acid

texts: During titration of $\ce{KMnO4}$ with $\ce{H2C2O4}$, can we use concentrated $\ce{H2SO4}$ or $\ce{HNO3}$ instead of bench sulfuric acid?


texts: What would cause a sudden drop in humidity in my home?

texts:
I have a ventless propane heater newly installed in my home, which has been an increasingly source of paranoia for me (constant condensation on the windows, worries about carbon monoxide poisoning).  It's been a interesting few weeks of trying to find the right balance of windows to crack; needless to say I'm looking for a new heater.
Today, I noticed that NONE of my windows had condensation on them, even though the heater had been running for hours and the relative humidity outside was 100% (~30F) with fog and sleet.  I would expect it to feel like a swamp in here.

Now for the chemistry question- I know that the incomplete combustion of propane in a low oxygen environment would produce carbon monoxide, but is it typical for the air to become more dry as well?  Does the lack of oxygen also produce less water, and maybe more H2 or something like that?  What would cause the unusual drop (or perceived drop?) in humidity in my house?


texts: How much additional hydrochloric acid should be added to arrive at ‘excess acid’?

texts:
I am an IB student. And I am trying to find the mass percentage of $\ce{NaHCO3}$ in antacid. I am dissolving the antacid in $\pu{0.1 M}$ $\ce{HCl}$ solution. So, first of all I conducted some preliminary experiments with pure $\ce{NaHCO3}$ powder to optimize the experiment, get a hang of it etc.

For this preliminary experiment, where I used $\pu{0.5 g}$ $\ce{NaHCO3}$, I calculated the amount of $\ce{HCl}$ solution required as being approx. $\pu{60 ml}$. Hence I added $\pu{100 ml}$ in the flask so that I have an excess of the acid as required.

Is adding $\pu{40 ml}$ as the supposed excess amount reasonable? Should it be more or less? I am confused because my teacher suggested that by even putting $\pu{100}$ ml of $\ce{HCl}$ in $\pu{0.5 g}$ of antacid tablets, I still don't have the acid in excess? But do I not? Doesn't it only take $\pu{60 ml}$ to neutralize $\pu{0.5 g}$ of $\ce{NaHCO3}$? So $\pu{100 ml}$ is definitely in excess, isn't it?


texts: Why aren't the Anton computers used more widely?

texts:
The Anton computers are purpose-built by DE Shaw research for molecular dynamics simulations. They achieve performance up to an order of magnitude faster than can be achieved with commodity hardware, but don't seem to be used all that much by the wider computational chemistry community. This is despite the fact that limitations on simulation timescales is a major impediment to using simulations to guide experiments, leading to all kinds of intricate theoretical methods to deduce longer-timescale properties from relatively short simulation trajectories.

Having read a bit about the Anton machines, which have been around for over a decade now, I'm perplexed as to why they haven't been more widely used. Is it because they are too inflexible, not available to enough researchers, not helpful in solving scientific problems, or is there some other reason I'm missing?


texts: Why do bubbles form on the side of a plastic bottle?

texts: I have a plastic bottle filled with drinking water where only one side of the bottle has air bubbles. I know that water is not pure and there are dissolved gases, and my theory is that there are small microscopic holes on one side of the plastic bottle that make bubble formation possible. Or may be its a temperature difference between the two sides (which shouldn't be the case - the bottle was kept in room temperature, but it was closed for a day or more). What could be the cause?


texts: What is the driving force for Claisen rearrangements?

texts:
I came across this mechanism (3,3 sigmatropic rearrangement). Why does the allyl vinyl ether have the ability to rearrange itself giving a new product? What drives the reaction?

Is it the instability of allyl vinyl ether (if yes, state why)?

Thank you in advance!


texts:
(1) $\ce{PH3(g) <=>[W]PH3(adsorption)->[W]P(s) + 3/2 H2(g)}$

The decomposition of phosphine on tungsten surface at low pressure is a pseudo first order reaction. This is because the rate of the reaction depends on the partial pressure of phosphine and which depends on the surface area of tungsten covered by phosphine.

$\ce{r= k.(P_{PH3})= k'*(covered surface area of tungsten)}$

But I am not able to understand the pseudo term used for the order of this reaction.

At high pressure, this reaction follows zero order kinetics due to complete coverage of surface area of tungsten.

Rate at high pressure= k

(2) The formation of any gas at low pressure on the surface of tungsten due to adsorption is zero order reaction.

At low pressure, according to Freundlich adsorption isotherm, the extent of adsorption varies linearly with external pressure as:

$\ce{x/m = k*p^{1/n}}$, where $\ce{x}$ and $\ce{m}$ are the masses of adsorbate and adsorbent.

Thus, the extent of adsorption is independent of the concentration of gas. Which means this is a zero order reaction.

Do in anyway (1) and (2) contradict?

(3) Is chemisorption a pseudo second order reaction because of involvement of chemical reaction in the rate determining step?
as mentioned here


texts:
I'm not an expert.

In simple words how do they differ:

$\ce{H-H-O}$ and $\ce{H-O-H}$ molecules?


texts: Calculating the solubility of aspirin in water

texts:
I am trying to investigate the relationship between the solubility of aspirin in water with the relationship to some variables. In my investigation, I seem to be stuck with the calculation of finding the solubility. Since reacting aspirin with aqueous NaOH affects solubility, one possible direction I considered taking is investigating the effects on the solubility by changing the amount of aspirin input. Or maybe keeping the aspirin input constant but change the amount of NaOH in the reaction. Either way, the calculation for the solubility is required, but how does one numerically calculate the solubility upon reacting with NaOH?

One way I found online, is dissolving aspirin into a conical flask. Titrate it with x amount of NaOH and record the final and initial volume of neutralization. Using the data, I would try and find the amount of dissolved aspirin in the flask, and basically, compare the amount with the amount stated for the tablet. But how will this give rise to the actual finding of the solubility? It will allow me to get the dissolved amounts, but is that the quantity of solubility? I heard solubility is grams/liter.


texts: What are Technetium's physical stress characteristics?

texts: I've looked at periodic and data tables from several sources, but none give mechanical / engineering property data on Technetium.  Why is this?


texts: What are good lubricants for Bunsen burners?

texts:
We've been running into a lot of problems the last several years with our laboratory Bunsen burners becoming jammed and/or corroded.  I've just come to find out that our lab tech has been lubricating the burners with glycerol, which seems wholly inappropriate to me. I guess she figured that if it worked for inserting glass tubing into rubber holes, it would work for anything. To me, something like a WD-40 would seem more appropriate based on household experience, but I'd like to hear if anyone else has found something for this exact application that works well for them.

I'm currently experimenting with white lithium grease.  An engineer friend also recommended Permatex anti-seize lubricant.  These seem to work well on a very short term, but we'll have to see how it holds up throughout the next several weeks.

Anyone have a favorite lubricant for something like this?


texts: How do I determine the crystal field splitting for an arbitrary point group?

texts: How can I figure out the degeneracy of the d orbitals for a site that has a given point group? Specifically I'm interested in $D_{3d}$ and $D_{3h}$, but it would be good to know how to do it in the general case.


texts: What exactly does it mean for the reaction of superoxide with non-radicals to be spin-forbidden?

texts:
From Wikipedia:

  The reaction of superoxide with non-radicals is spin forbidden. In biological systems,   this means its main reactions are with itself (dismutation) or with another biological radical such as nitric oxide (NO) or with a transition-series metal.

I know that one of the configuration bands is paired, and one is unpaired. Does the unpaired one have to bond with an unpaired one from another radical? What does this also say about reactions of the excited state of singlet oxygen (shown in the middle below) with non-radicals?

Also, is superoxide a doublet?


texts:
Oobleck is basically a mixture of cornstarch and water. It has the interesting property of going hard when pressure is applied. For example, it feels like a liquid when you swirl your fingers through it, but it becomes hard for a second if you punch it.

The common explanation for this is that the starch-water mixture is a suspension, and the  starch particles "lock" when pressure is applied.

What exactly is the mechanism of this "locking"?


texts: Has the molecular diatomic oxygen trianion been observed or predicted?

texts:
Has diatomic oxygen ever been observed with a 3− charge, i.e. $\ce{O_2^{3-}}$? Have any ab intio calculations been done on this ion?

Update:

Just to summarize some of the answers below and add my two cents, it seems that no studies have reported observing this ion experimentally, either in isolation or as part of a condensed phase. Ab initio calculations suggest that $\ce{O_2^{3-}}$ is unstable in isolation, meaning that the loss of an electron is exothermic. However, first-principles calculations have predicted that a molecular oxygen trianion can exist as part of a solid; see Phys. Rev. B 85, 035210 (2012).


texts: Why are pi antibonding orbitals lower in energy than sigma antibonding orbitals?

texts: I know when a carbonyl group is attacked by a nucleophile, the electrons of the nucleophile enter the antibonding π orbital of the $\ce{C=O}$ bond, which breaks the π bond. My textbook says that it enters the antibonding π orbital instead of the antibonding σ orbital, because the antibonding π orbital is lower in energy. This is my point of confusion: why is it lower in energy?


texts: Why distinguish between polarity and hydrophobicity?

texts: I have yet to see an example of a molecule that's both polar and hydrophobic or that's both non-polar an hydrophilic. If no such molecule exists, why use the terms "hydrophilic" and "hydrophobic" at all if we can just refer to them as being polar or non-polar? If there are such molecules, what are some examples and why do they exhibit non-polarity and hydrophilicty, or polarity and hydrophobicity?


texts: Why don't alcohols undergo nucleophilic substitution with ammonia?

texts: Alcohols can undergo nucleophilic substitution with $\ce{PCl5, POCl3, HCl}$.  Halogenoalkanes can undergo nucleophilic substitution with $\ce{NH3}$. The $\ce{C-O}$ (in alcohol) and $\ce{C-Cl}$ (in chloroalkanes) bond energies are comparable. Why don't alcohols undergo nucleophilic substitution with $\ce{NH3}$?


texts: Why do we scratch the walls of test tube in test for magnesium or calcium basic radicals?

texts:
In test for calcium ion, we add ammonium carbonate in presence of ammonium hydroxide and then white precipitate (of $\ce{CaCO3}$) is formed which is dissolved in acetic acid and then reacted with ammonium oxalate to form $\ce{CaC2O4}$. But it says you have to scratch the walls of the test tube to get the precipitate. Why is it so?

Similarly, for magnesium ion we add ammonium hydrogen phosphate to get white precipitate. For this reaction too, the walls of the test tube are to be scratched to get the precipitate.

I read somewhere that scratching creates a surface for recrystallization of the precipitate. I just don't really understand what does it mean. Can someone explain it?


texts: I have learned about metal and their reactivity series. However, why metals have different reactivity? What are the factors of different reactivity rate for metal? All I can think of is the number of electrons which causing it.


texts: Lewis structures of molecules containing oxygen

texts:
As far as I know, when writing Lewis structures for molecules, we need to consider the octet rule and the valence electrons each atom has.

But, if we take for example, the molecule $ Cl O_2^- $ , we have the following Lewis structure: (as it appears here )
O - Cl - O with 6 valence electrons surrounding each oxygen atom, and 4 valence electrons surrounding the chlorine atom.

My problem is:
The oxygen atom has 6 valence electrons. By forming a chemical bond with the chlorine atom, it shares one electron, which leaves it with a total of 5 non-bonded electrons. So, how can it be that in the Lewis structure of this molecule, it has 6 non-bonded electrons and one shared electron? (or a total of 7 electrons! )


texts: How to calculate Wiener index for aromatic and cyclic organic compounds?

texts: I have been searching for literature on calculating the Wiener index for aromatic and cyclic organic compounds. For acyclic aliphatic compounds the methodology is straightforward obtained from obtaining the distance matrix of molecules . However, for aromatic and cyclic compounds is there a general methodology in obtaining the Wiener index?


texts: Why isn't ammonium strong acid, since it's charged and ammonia is neutral?

texts:
Why is ammonium such a weak acid $(\mathrm pK_\mathrm a = 9.24)$, if $\ce{NH4+}$ has a positive charge on nitrogen, while $\ce{NH3}$ is neutral. It means that conjugate base (ammonia) is really stable, which makes conjugate acid a strong acid.

Another argument why ammonium should be strong acid is comparison with hydronium ion $\ce{H3O+}$. Both nitrogen (EN = 3.04) and oxygen (EN = 3.44) are significantly electronegative atoms and "don't like" to be positively charged. That explains pretty good hydronium ion $\mathrm pK_\mathrm a = -1.74$, but why is then ammonium $\mathrm pK_\mathrm a$ is just $9.24$?


texts: How can silver work as a disinfectant in a bathtub if precipitates in the presence of chloride?

texts: I use a silver based disinfectant in my hot tub. It is in the form of silver nitrate beads. There is chlorine in the tub that I presume becomes chloride ion. Why doesn't the silver form a precipitate of silver chloride in the water?


texts: What substance consumes oxygen from atmospheric air

texts:
I'd like to find an economical substance that will consume oxygen from a container. Steel wool comes to mind but I don't have an intuition how feasible it would be.

The chamber is 5 gallons in size and I'd like the oxygen to be consumed in 48 hours or less.


texts: Is it tennessINE because it has 117 electrons or because it behaves like a halogen?

texts:
The NPR News podcast and transcript The Convoluted Story Of How The First Atoms Of Tennessine Were Created includes the following exchange between science reporter Joe Palca and Oak Ridge nuclear engineer Julie Ezold:

PALCA: In other words, in five months, they only got six atoms of tennessine. When I first heard that name, I thought it was a mistake. All the other synthetic elements ended in -ium - think plutonium or americium. Oak Ridge nuclear engineer Julie Ezold understands my confusion.
JULIE EZOLD: We all thought it was going to be that way as well. But remember - the periodic table has rules.
PALCA: Ezold says Element 117 fits in a column of the periodic table filled with compounds called halogens - fluorine, chlorine, bromine.
EZOLD: Therefore, its name had to end in -ine. So instead of tennessium (ph), it's tennessine.

The more I thought about this, the more I questioned how elements discovered in the future might or might not be classified as halogens, especially if an "island of stability" is ever found and even more elements are discovered.

Is there really a rule or at least a firm guideline that ultimately requires the name of element 117 to end in -ine simply because it has 117 electrons?
Or was it somehow necessary to experimentally demonstrate some chemical property associated with halogens?
Or would an atom with 117 electrons certainly and without question behave like a halogen?
Or will all current and future elements that obeys certain numerical rules be called halogens no matter how they behave chemically?


texts: Why does a proton prefer to attack a double bond instead of protonating an alcohol in a reaction of unsaturated alcohol with sulphuric acid?

texts:
A solved problem in Organic Chemistry by Solomons, Fryhle and Snyder asked to write the mechanism for the following transformation in the presence of sulphuric acid ($\ce{H2SO4}$):

The mechanism provided by the book is as follows:

It can be seen that a proton from sulphuric acid attacks the double bond thereby forming a tertiary carbocation as an intermediate. Later the lone pair on the oxygen atom of the hydroxyl group attacks the carbocation to form a cyclic intermediate which after deprotonation gives the required product. I understood the mechanism given in the book.

However, when I attempted the problem with the given reactant and the reagent, instead of attacking the carbon-carbon double bond, I protonated the alcohol. I attained at a much different product by following the mechanism given below:

The reason I chose to protonate the alcohol was I felt that electron density near oxygen is much higher than that in the double bonds. Moreover, I also end up with a conjugated diene, which is resonance stabilized.

Further, the following statement given as an explanation for a different problem supports my method of protonating over attacking the alkene:

  Protonation of an alkene forms a carbocation with an open octet, whereas protonation of methanol does not form an open octet. Therefore, we predict methanol to be a stronger base than alkene. The mechanism starts with the reaction of a stronger base with sulphuric acid.

Now, my question is, why does a proton prefer to attack a double bond rather that protonating an alcohol? Under what conditions, does a proton protonate the alcohol instead of attacking the double bond? Are there any well-defined rules to predict which attack will be preferred over the other in such cases?

Image source: I made them using ChemDoodle.


texts: Why does iodine exhibit metallic properties at room temperature although being a non-metal? Are there any similar elements like this?


texts: Gas / Gas mixture dynamic viscosity temperature and pressure dependance

texts:
I’m trying to get an accurate interpretation of certain gases ($CO_2$, $N_2$, $NO$, etc.) dynamic viscosity [Pa.s] as a function of temperature and pressure (afterwards determine the dynamic viscosity of the whole gas mixture).

I have found more than one equation and I’m struggling to choose a proper one which can be interpreted in MS Excel. For example, it’s not that easy to find all the coefficient for each equation (unfortunately, same goes for the gas mixture dynamic viscosity: there is Sutherland-Thiesen (found on the internet), Herning–Zipperer (found in the literature) equation, etc. …).

Thanks for any help.