texts: Recently, I have come across a problem, in which a ketone needs to be converted into an alkene. However, in the alkene product, there is also another bromide functional group, at the end of the alkyl chain. I was thinking of using a dibromide (an alkyl chain with bromine atoms at both ends) and performing the Wittig reaction. However, I foresee that both bromide functional groups would participate in the reaction. Would one solution to this be to use a protecting group? Or would the problem be solved if I manipulate the stoichiometry of the reactants (e.g. ensure that the dibromide is in excess etc.)?


texts: If I can smell an object, it means that molecules of it are getting separated from it, so they can reach my nose. As far as I know, metals don't sublimate, especially not in room temperature. However, copper has a very strong and characteristic smell. Does it mean that copper will degrade pretty quickly, or are just we so sensitive to it that a few molecules are sufficient? I assume it has to do something with oxidization, but it doesn't oxidize that much naturally as other metals, for example, iron.


texts: Why is are weak acid-strong base and strong acid-weak base reactions irreversible?

texts:
In the case of both are strong, I can see why it's irreversible, because the acid is very willing to give a proton and the base is very willing to take one.
Now here are my two main questions:

In the case of both are weak, we say the reaction is reversible. Does this mean the reaction happens then the products react again to give reactants, or that the reactants don't run out and the reaction doesn't happen at "full potential"?
In the case of a reaction between a strong base and a weak acid (or the other way around), why is it always irreversible? I mean since one of them is weak, shouldn't it give out an unstable product which is willing to react again, like

$$\ce{CH3COOH + OH- → CH3COO- + H2O}$$

The $\ce{CH3COOH}$ is a weak acid. The $\ce{CH3COO-}$ isn't stable so shouldn't it react again?


texts: Strengthening a clay rocket nozzle with sodium silicate and calcium chloride

texts:
"I strengthen the bentonite clay nozzle by dipping the rammed nozzle in a $50\%$
 sodium silicate solution and allow to dry in warm oven. Then dip in a strong solution of Calcium Chloride, again dry. Then another dip in $50 - 70\%$ sodium silicate and again air dryed in warm oven. A third silicate treatment can be done. This makes for a strong nozzle that doesn't erode unless the motor thrust is over about $\pu{150kN}$." My question is: What is going on here chemically? Is it crosslinking?


texts:
I wonder if and how long (approximately) it will take for benzalkonium chloride (shown above; $n = 8, 10, 12, 14, 16, 18$) to breakdown (degrade fully or partly) in a closed water loop with continuous flow and a volume of approximately $1.5\ \mathrm{L}$ distilled water.

The concentration will be around $2\ \mathrm{ppm}$ to $10\ \mathrm{ppm}$.

UV and general light will be kept to a minimum but can't be fully shut out. The temperature will flucturate between $19\ ^\circ\mathrm{C}$ to $50\ ^\circ\mathrm{C}$.

Thank You!


texts: Doesn't the fact that the lone pair on the nitrogen in amides occupy a p orbital contradict Hund's rules?

texts: Since the $\ce{sp^2}$ hybridized orbitals are lower in energy than the p orbital shouldn't the $\ce{sp^2}$ orbitals fill first? Why is this not the case - two electrons fill the p orbitals while all three $\ce{sp^2}$ orbitals are singly occupied? If you look at Carbene (CH2) it's $\ce{sp^2}$ hybridized with a lone pair in one of these orbitals. However, the higher energy p orbital is empty - as would be predicted is Hund's rules are followed. Is it something to do with the conjugation in amides?


texts:
A question in an exam was as follows:

Iodine reacts with ozone gas to form a dark yellow solid $\ce{X}.$ Let the number of lone pair of electrons in un-ionised form of $\ce{X}$ be $m,$ number of lone pair of electrons in the anionic moiety of $\ce{X}$ be $n$ and the positive charge on the cationic moiety of $\ce{X}$ be $p$ units. Then what is the value of $\displaystyle\frac{m - p}{n}?$

This reaction of iodine with ozone is:
$$\ce{I2 + O3 -> I4O9 <=>I^3+(IO3^-)3}$$
Therefore the anionic moiety is $\ce{IO3-}$ and cationic moiety is $\ce{I^3+}$. However the first part of the question states un-ionised form. My assumption is that this is $\ce{I4O9}$ and they ask for the number of lone pairs on the molecular form.
The answer to this question takes into consideration that $\ce{I4O9}$ is an equimolar mixture of $\ce{I2O4}$ and $\ce{I2O5}$ which gives the answer to be $2.5$
However, from the abstract of J. Raman Spectrosc. 1985, 16 (6), 424–426:

The Raman spectrum of $\ce{I4O9},$ formed by the gas‐phase reaction of $\ce{I2}$ with $\ce{O3}$, has been measured. Freshly prepared samples of $\ce{I4O9}$ gave broad band spectra characteristic of an amorphous solid. Vibration bands at $780,$ $740,$ $620$ and $\pu{450 cm−1}$ were observed. It was established conclusively that $\ce{I4O9}$ is a distinct molecular species and not a mixture of $\ce{I2O5}$ and $\ce{I2O4}.$

If $\ce{I4O9}$ is a distinct molecular species, what is the molecular structure of $\ce{I4O9}?$


texts: How can copper(II) sulfate crystallize outside a glass vial?

texts:
I'm making copper sulfate crystals in glasses. Within a few weeks, the copper sulfate seems to crystallize both inside and outside the glass:

(A few weeks after making a new solution)

(Yet another few weeks later)

How is that possible? The glasses haven't moved for all those weeks. Is that pure capillary action, or is there another phenomenon?


texts:
On adding $\ce{BaCl2}$ solution to $\ce{ SO4^{2-}}$ salt aqueous solution $\ce{ BaSO4}$ is formed as a white precipitate, which confirms the presence of the anion.

While doing the test in my school laboratory, we were given a list of procedures to follow; for $\ce{ SO4^{2-}}$ it read:

'Experiment: Aqueous solution of sample + dilute $\ce{ HCl}$ + $\ce{ BaCl2}$ solution

Observation: white ppt'

Why do we need to add $\ce{ HCl}$?


texts: Why isn't ammonium chromate called diammonium chromate?

texts: I have to name $\ce{(NH_4)_2CrO_4}$. I know the answer is ammonium chromate. But I don't understand why it isn't called diammonium chromate.


texts:
Very basic question here, but I'm confused why Delta-H seems to be the reverse of what I would expect for bond enthalpy. For example, here's a problem in my textbook where the goal is to find delta-H:
$$\ce{H2(g) + Br2(l) -> 2HBr(g)}$$
Using the table I have, I see that an $\ce{H-H}$ bond has an average enthalpy of 436, $\ce{Br-Br}$ has 193, and $\ce{H-Br}$ has 366. 436+193 = 629, and 2*366 = 732, so the reactants have a total of 629, compared to the products, which have 732.
My intuition (and Google, as far as I can tell) would tell me that, because the H value increased when the reaction occured, the answer would be positive 103. But my textbook says the answer is -103. This makes no sense to me - what am I missing here? Why do all the Delta-H (AKA Change in H) values seem to be negative what you'd expect?


texts: Interpretation of Carbon-13 NMR Spectra for Chemically Similar Carbon Atoms

texts: I am analyzing the Carbon-13 NMR data from a reaction I will be modifying. There is not NMR data available for the specific compound I am attempting to synthesize; however, the compound I am synthesizeing only differs by the number of carbon atoms on the acyl group (from a Friedel-Crafts acylation). The compounds I will be synthesizing and analysing are 1-(5,7-dimethoxy-2,2-dimethyl-2H-1-benzopyran-8-yl)butanone (1) and 1-(5,7-dimethoxy-2,2-dimethyl-2H-1-benzopyran-6-yl)butanone (2) respectively. The compounds synthesized in the protocol I am following were 1-(5,7-dimethoxy-2,2-dimethyl-2H-1-benzopyran-8-yl)ethanone (4a) and 1-(5,7-dimethoxy-2,2-dimethyl-2H-1-benzopyran-6-yl)ethanone (4b) respectively. I will include images below. 14 peaks are expected from each of the carbon-13 NMR spectra since each carbon is chemically different; however, compound 4 only showed 13 NMR peaks. My hypothesis was that this was due to the fact the the methoxy carbons are so chemically similar that they appear as a single peak; however, I am not sure if this is the case. I expect that I can use this to my advantage in distinguishing compounds 1 and 2 when I synthesize them. The doi to the article is: 10.1016/j.bmc.2018.05.016. I will also include the NMR data below:


texts: Uncertainty in measuring the mass of the palm oil and the base in saponification

texts:
I am a student coming from the domain of mathematics, and I am working on error analysis and uncertainty, but I have a question  in the domain of chemistry.
I am  studying the effect of the measurement error in saponification.  According to different research references (this is one) we need $\pu{142 g}$ of $\ce{NaOH}$  to react with  $\pu{1000 g}$ of palm oil to produce soap.

What if we use  $\pu{140 g}$ of  $\ce{NaOH}$  with  $\pu{1000 g}$ of palm oil? Would this change the mass of the obtained soap? Or would it just change the quality of the soap?


texts: Green Potassium Manganate and Sodium Hydroxide Equation

texts:
When a sample of green potassium manganate (VI), $\ce{K2MnO4}$, is added to aqueous sodium hydroxide, a brown black solid A and a purple solution of B are obtained.

I know that the brown black solid A is $\ce{MnO2}$, but I can't seem to write out the entire equation.

Can someone help me with this?

Thanks! Really appreciated.


texts: How to choose a proper chromatography way to separate substrates?

texts:
I'm a freshman and I recently learned how to do TLC and column chromatography. I also know a little about other ways to separate things by chromatography, such as affinity chromatography, gel chromatography, ion exchange chromatography, and gas chromatography, but without many details.

I am facing problems in solving a question requiring us to judge how to separate these combinations of substances by chromatography (if there was no such confinement, this will be much easier):

  N-phenylethanamide, N-phenylpropionamide
  methoxymethane, ethoxyethane
  Aβ36，Aβ42 (Aβ is a kind of peptide which is related to Alzheimer's disease, while the number, 36 and 42, refer to the amount of amino acids polymerized in the peptide)

Here are the specific issues I've met：

I've no idea how to deal with the first combination since their difference seems to not be significant, no matter in polarity, acidity (basicity), or molecular size. Is there any other chromatographic way, or did I get something wrong?
I think I can deal with the second combination by gas chromatography, since they are both volatile. But I'm not sure if it is a good idea. Is there a better way or not?
I've found some description for the separation of different Aβ, suggesting that the following ways are usually used: use antibodies (e.g. ELISA) or electrophoretic separation (e.g. PAGE). But seems that neither ways are related to chromatography. It is also said that reverse phase liquid chromatography after CNBr cleavage works, but this way is complex and time consuming. I'm wondering (a) if I can use antibodies or something else to deal with it by affinity chromatogrphy and (b) how CNBr works? (Now I know CNBr is used to cut proteins/peptides at where methionines are, but still not knowing how reverse phase liquid chromatography works.) Also I want to ask if there is a better way as well.


texts: Why carbon nanotubes can act as a good electrical conductor?

texts:
Bulk carbon is an insulator, but at nanoscale (e.g. carbon nanotubes) carbon may become a good electrical conductor. If I am correct this means  carbon nanotube band structure is metal-like. E.g. it has partly filled valence band (like in the rightmost case in the figure below).

At nanoscale materials are influenced by quantum confinement. Because of quantum confinement semiconductor nanoparticle has higher band gap and discrete energy levels compared to bulk semiconductor (see the figure about quantum confinement below).

I am assuming that quantum confinement phenomenon also occurs for carbon at nanoscale. Then, how certain carbon nanotubes can show good electrical conductivity?


texts: When to use internal energy and enthalpy in balances

texts: I am confused as to when you use ΔU and when to use ΔH, I don’t really understand the difference. Is it that ΔU is used for closed systems whilst ΔH is used for open systems?


texts: Can I add the molarities of multiple solutes together?

texts: If I am calculating the molarity of a solution in which more than one solute is dissolved, can I add the total number of moles of all the solutes together and divide it by the total volume of solvent to get the molarity of my solution?


texts: Can a substituted cyclohexane progress through SN1?

texts:
I have read that when the leaving group substituent is stuck in the equatorial position for some reason (like from a t-butyl group or a trans decalin), SN2 is either very slow or just doesn't happen at all because the rear attack is hindered by axial hydrogens/other substituents. I haven't been able to get a straight answer as to whether it can instead progress through SN1 at an acceptable rate, since the attached carbon will at least be secondary.

The only thing I can think of which would prevent this happening is the difficulty of forming a planar sp2 carbocation in a such a rigid system.

Any help is appreciated, thanks.


texts: Assignment of the 13C NMR spectrum of 1-(ferrocenyl)ethanol

texts:
The molecule in question has the following structure:

(source: sigmaaldrich.com)
The 13C NMR is given below:

My assignments are:
23.700 ppm, -CH3
65.569 ppm, CH adjacent to the -OH
66.138/66.183 ppm; 67.924/67.977 ppm, substituted Cp carbons with protons attached
68.344 ppm; Cp carbons
94.857 ppm; Quaternary C
Are these assignments correct? The Cp carbons usually appear between 80-95 ppm but they are shifted down for some reason (I'm not sure why).
Additionally, why are the substituted Cp carbons (non-quaternary) doublets? I thought it may be due to the presence of staggered/eclipsed forms of the molecule but this would affect all the carbon environments.


texts:
In a battery, I don't understand what makes the element in the anode separate from the anode to become a positive charge in the electrolyte and leave some electrons inside the anode.

Also, why does the molecule separated from the anode leave electrons on the anode?


texts: What does "oxidized form" and "reduced form" mean?

texts:
What does the phrase "oxidized and reduced forms of the reactants" mean?

For some context: The book was talking about half-reactions in a half-cell of a galvanic cell, and it said this,

  Sometimes, both oxidized and reduced forms of the reactants in a half-cell are soluble and cannot be used as an electrode.

I am confused as to what the "oxidized and reduced forms of the reactants in a half-cell" might mean because in a half-cell either only oxidation or reduction takes place.


texts:
I have the following problem:

  A polypeptide has the following sequence (amino end on the left)
  $$\mathbf{lysine - aspartic~acid-histidine-arginine-serine}$$

  Using the $pK_a$ information that follows, what would be the approximate charge on this molecule at pH = 3.3?

  $pK_a$ values for the various groups in the molecule are as follows:

  \begin{array}{|cc|}\hline
\rm Alpha~carboxyl & 2.2 \\ \rm Alpha~amino & 9.5 \\ \rm R-group~amino & 11.7 \\ \rm R-group~carboxyl & 4.5 \\\hline\end{array}

After my calculations I got +2 and my answer was wrong. How to solve it correctly?

My effort:

$\ce{NH3}$ has $+1$ when on and $0$ when off. $\ce{NH3}$ are Lysine, Histadine, and arginine.
$\ce{COOH}$ has $0$ when on and $-1$ when off. $\ce{COOH}$ are Serine and aspartic acid.
Based on the pH and $pK_a$ values the answer should be 2.
Lysine=+1 Aps=0 His=+1 Arg=+1 Serine=-1


texts:
The following structural formula (source: Wikimedia) is labelled ᴅ-amphetamine:

A Fischer projection of this molecule would contain, I think, the following line:
$$\ce{H2N-C-H},$$
and I would have labelled the molecule therefore as ʟ-amphetamine.
Why am I wrong? Why is it called ᴅ-amphetamine?


texts: What is the enthalpy of formation of 1 mol of sulfuric acid?

texts:
In the contact process, the commercial process of producing $\ce{H2SO4}$, several reactions occur before the final product is produced:

  \begin{align}
\ce{S8(s) + 8O2(g) &-> 8SO2(g)} &\Delta H_\mathrm{f} &= \pu{-70.9 kcal mol^{-1}}\tag{1} \\
\ce{2SO2(g) + O2(g) &->[V2O5] 2SO3(g)} &\Delta H_\mathrm{f} &= \pu{-94.5 kcal mol^{-1}}\tag{2} \\
\ce{SO3(g) + H2O(g) &-> H2SO4(g)} &\Delta H_\mathrm{f} &= \pu{-193.9 kcal mol^{-1}}\tag{3}
\end{align}

  Given that $\Delta H_\mathrm{f}$ for $\ce{H2O(g)}$ is $\pu{-68.3 kcal mol^{-1}}$, what is the enthalpy of formation of $\pu{1 mol}$ of $\ce{H2SO4}$?

What I've tried to do:

Summing all the enthalpies, I arrived at to $\Delta H_\mathrm{f} = \pu{-427.6 kcal mol^{-1}}$.
Using the data from equation $(3)$, I conclude that the answer is $\Delta H_\mathrm{f} = \pu{-193.9 kcal}$.


texts: In the Nernst equation, does T refer to the temperature of the standard cell or the cell under non-standard conditions?

texts: I am doing an experiment where I am varying the temperature of the electrolyte of the anode half cell. I am trying to calculate the cell potential using the Nernst equation under standard conditions but I'm not sure what T to put in.


texts: Separating specific components of a PUREX raffinate

texts:
The PUREX extraction in nuclear fuel reprocessing leaves behind a nitric acid raffinate full of (mainly) 'fission products', which are a diverse set of elements produced by fission in a nuclear reactor. The concentrations of the various components of the raffinate are shown in this image.

My goal is to separate out the group III elements from the group IV+ elements (shown highlighted in red/blue). It does not matter what happens to the rest of the components, they can go with either or neither of these groups in any combination, all that matters is that the group III elements are spatially separated from the group IV+ elements. The process can be as inexact as necessary as long as it mostly accomplishes this goal.

Any thoughts? My nuclear chemistry book says that these group III elements are "have soluble nitrates, chlorides, and sulfates while their fluorides and hydroxides are insoluble. LaF3 is frequently used as a carrier for this group. They form stable complexes with strong chelating agents such as DPTA, EDTA, and the like". Perhaps this makes the question fairly straightforward, I'm coming from a physics, not a chemistry background. I'm just confused as to what properties the group III elements have that the group IV+ elements don't which could be leveraged to achieve some kind of separation.

Sorry for the wall of info, and thanks very much in advance for any help or input!


texts: How is it possible, that the hydrolysis of ethers proceed via a SN2 mechanism?

texts:
Ethers on hydrolysis with dilute $\ce{H2SO4}$ under pressure produce alcohols.
This is basically a type of acidic cleavage of ethers by the SN2 mechanism.

(source)

There is inversion of configuration.
Now if $\ce{Nu}$ is $\ce{OH-}$ its called hydrolysis of ether.

Is it right, that for SN2 the leaving group must be more stable than the approaching group? In case of ether hydrolysis the leaving alkoxy group is less stable than the entering $\ce{OH-}$ group.

So how does the reaction succeed? Can someone please explain?


texts: Ionic radius for tetrahedral metal–ligand complexes

texts:
The ionic radii for metal–ligand complexes that are in an octahedral coordination are easy to find. I understand that when the $\mathrm{e_g}$ orbital is filled, the ionic radius increases because the electrons repel the ligands meaning the ionic radius increases.
But I am not sure about tetrahedrally coordinated metal–ligand complexes. I think it might be the same for the first two to three electrons, but since the $\mathrm{t_{2g}}$ orbital electrons are degenerate, the $Z_\mathrm{eff}$ might be stronger “felt” by the ligands.


texts: Molecular orbital diagram and irreducible representations for dinitrogen

texts:
I'm trying to understand how to draw molecular orbital diagrams, since I'd like to use the molecular orbitals to determine the total state of the molecule (i.e. $A_1$, $B_1$ etc.), so I prefer the notation with irreducible representations of orbitals like it's shown in this video for $\ce{H2O}$.

The problem is that I'm not sure how to make molecular orbitals for $\ce{N2}$ and $\ce{N2^+}$.

I know that $\ce{N}$ has atomic orbitals $\ce{1s^{2} 2s^{2} 2p^{3}}$. $\ce{N2}$ is a linear molecule, so it belongs to the $D_{\mathrm{\infty h}}$ symmetry point group, but we can descend in symmetry, so we'll use $D_{\mathrm{2h}}$.

But now I have no idea how to proceed. Should I work with both nitrogen atoms together, i.e. with group orbitals, similarly to the case with two hydrogen atoms in $\ce{H2O}$? Or am I supposed to work with them separately?

So could you please write down one of the diagrams using irreducible representations and explain it step-by-step? I think it would be really useful here, as I couldn't find any source with some general explanation.


texts: What does the hydrolysis of a salt tell us about its basic/acidic character?

texts: I'm curious to know how basicity and acidity arises when a salt or covalent compound is dissolved in water.


texts: What is deuterium-depleted water actually used for?

texts:
I noted, flipping through the paperback Alfa Aesar catalogue today, that they sell deuterium-depleted water. Under the usage category, they list 'NMR'. I'm trying to work out what specific use this water has. Unfortunately, on the basis of very limited clinical evidence of improved cancer outcomes I've been bombarded mostly with companies recommending deuterium depleted water for drinking, which trips my snake oil sensor and is something I doubt Alfa has in mind (at US$1930 per liter, and a US RDI of 3.7 L/day for an adult male, that would seem to be a comically expensive drinking habit.)

I suspect biophysics experiments are a small part of the market for this water, but that there's some other NMR-related use I can't think of, possibly calibration related. What is it?


texts: Forms of Henry's law versus ideal gas law

texts:
This might be a slightly daft question as I'm a physicist rather than a chemist, but I have a slight problem in using Henry's law which I think I can circumvent using the ideal gas law – I'd be grateful if anyone can confirm or deny my logic!

I have an equation that yields the volume of oxygen gas per unit mass of tissue. We'll call this quantity $C$ with S.I units of $\mathrm{m^3\: kg^{-1}}$. We also have the partial pressure $p$ measured in $\mathrm{mmHg}$ and we wish to relate the two; several texts have suggested using Henry's law of the form $C = kp$ where $k$ is Henry's constant for oxygen. However, this causes a problem, as I can find no form of Henry's law with the correct units to allow this conversions (units of $\text{vol} / ({\text{pressure} \times \text{mass}})$).

My first question is does such a series of constants exist and does anyone know where?

In the interim, I decided to try to circumvent this problem by using the ideal gas law, which I believe holds at the relatively low pressures in very shallow water. Knowing one mole of oxygen gas has a mass of $32\:\mathrm{g}$, and occupies a volume of $22.4\:\mathrm{l}$ at standard temperature and pressure of $760\:\mathrm{mmHg}$, I re-wrote the expression for the mass of $\ce{O_2}$ in a given volume;

$m_{\ce{O_2}} = \frac{0.024\,p}{(0.032)760RT} = \frac{0.7\,p}{760RT}$

Using the ideal gas constant, and a temperature of $310.15\:\mathrm{K}$, I get

$m_{\ce{O_2}} = 3.572 \times 10^{-7} \cdot p$

If I define $M_{\ce{O_2}}$ as the unitless mass fraction of $m_{\ce{O_2}}$ per unit mass, then knowing the density of oxygen gas is around $1.331\:\mathrm{kg/m^3}$, I can divide this into $M_{\ce{O_2}}$ to get the expression

$C = 2.6835 \times 10^{-7} \cdot p$

which has the correct units. My second question is then is this valid, and if not, why not?


texts: How do you purify phosphoric acid from cheap commercial (hardware-store) products?

texts: I am looking for idea's on how to purify phosphoric acid for lab use, as the the price for reagent grade V's home-use ended with me buying a product designed as a rust-killer for steel... The percentage is actually quite high in this product (being 40%), but the unlisted agents added are obviously not going to result in any useful outcomes in lab use.. Has anyone got any ideas on safe purification method's in this case?


texts: Calculated 13C NMR Shifts of brominated Carbons

texts:
Since I calculate NMR spectra for a while by simply using one of recommendations by CHEmical SHIft REpository:

mPW1PW91/6-311+G(2d,p)-SCRF//B3LYP/6-31+G(d,p)

without thinking to much how it actually works*, there is a common misprediction that I'd like to understand.

It seems to be that the shift/shielding of the brominated carbons is always way off the measured shift. Compared to all other "normal" substituted carbons (C, H, O, N...) it is also far from being predicted good.

Luckily for me, as I don't want to show my own molecules :D, the Repository gives an example (Aplydactone) with a brominated carbon that shows exactly what I mean:

The overall $^1$H Mean Absolute Deviation (MAD) is about 0.08 ppm and for the $^{13}$C shifts the MAD is about 1.5 ppm but without the brominated carbon (right side of picture). The predicted shift has a failure of 12.25 ppm (measured 65.5 ppm vs. calculated 77.75 ppm) which is about ten times the MAD of all other carbon shifts.

Is there a common explanation for that? Is it simply that there were no brominated samples within the test set or is there a much deeper reason? Like Bromine must be treated with a different/super special basis set or sth similar.

This comes right now into my mind ... As there might already be some influences of the relativistic effect, could that be a reason?

Please tell me of your deeper insight into the calculation of NMR shieldings that could yield to this misprediction that I either understand how to correct those errors or that I at least have an explanation.

I did no further research throughout the internet yet, as I have not much time right now. But as this question keeps in my mind, maybe someone of you has done the research and would share it with me.

* I know that it uses a regression function which was calculated through comparing lots of experimental vs. predicted shifts for a bunch of small organic substances. What I mean is more the quantum theoretical aspect.


texts: Why is grease from cooking hard to remove from wood?

texts:
Cooking oil that jumps from a frying pan in use and over time accumulates around the frying pan on a wooden surface is sticky and hard to remove.

My question is why. Why is it hard to remove? What is the chemistry behind it? Does it bond with the wood somehow? If so, how is it different from oil used to give the wood a protective coating? Why is one sticky and the other not sticky?


texts: Why does the Grignard reagent of CH3I can only be prepared using diethyl ether as solvent but there is no reaction when using THF?

texts: Does anyone know why Grignard reagent of CH3I can only be prepared using diethyl ether as a solvent and yields no reaction when developed in THF? Theoretically, I is the most reactive halogen for Grignard reactions, so using THF or diethyl ether should make no difference.


texts: What does "electrochemically active species" mean in the expression for the mass-transfer limited current?

texts:
The expression for the mass-transfer limited current $i$ is given by
$i = nFAmC$.

where $C~[\mathrm{mol\, cm^{-3}}$] represents the concentration of the electrochemically active species that gets converted at the electrode; if the entire analyte gets converted, then $C$ is equal to the initial bulk concentration of the analyte.

I am confused as to what electrochemically active species mean? Is that just saying the ions in solution? Or is it the oxidized ion and the reduced ion?


texts: Derivation of mean speed from Maxwell–Boltzmann distribution

texts:
I found that if a velocity of a gas follows the Maxwell–Boltzmann distribution, the mean velocity is given by
$$\langle v \rangle = \sqrt{\frac{8RT}{\pi M}}$$
where $R$ is the gas constant, $T$ is temperature, and $M$ is molar mass. How would one obtain this result from the Maxwell–Boltzmann distribution?


texts: I have a molecule that is 8% of the R groups are replaced with Acetyl groups.  When I dissolve it in water it drops the pH.  I am trying to understand why.


texts: Interaction between Ozone and Carbon Dioxide

texts: We are trying to predict what will happen when carbon dioxide gas is introduced into a contact chamber that serves as an ozone contact chamber. These contact chambers presently oxidize compounds found in municipal pool water along with chlorine at below 5 ppm. There are 3 contact chambers (one for each pool) and the temperature range is from 104 to 80 F. We are switching from hydrochloric acid to carbon dioxide to keep the total alkalinity from dropping when the acid is introduced.


texts: Why is predicting products of chemical reactions difficult?

texts:
I was going to ask whether there are software that could be used to predict the products of any given chemical reaction. However, I then noticed these two earlier questions

Chemical software for solving reactions
Software for predicting chemical reactions

where it is said such predictions are too difficult to make. What makes the prediction difficult?


texts:
If we look at the bond angles of O-N-O in figure (c), (D) and (F), there not too much change in bond angle. Even though they are notable.

So my question is,

Why do we observe very small change in angles?


texts: Conductivity measurements of demineralized water - Unexpected results. Looking for explanation

texts:
I'm trying to measure the conductivity change of demineralized water over a few days. But I get results I can't explain.

Setup

This is the circuit and cell I'm using:

Where $R_x$ is the conductivity cell, R is $1797 \Omega$.
The right picture shows the cell ($R_x$). The metal plates shown (barely visible) are made of stainless steel.

Evaluation

On ch 1 and ch 2 I measure the voltage by consecutively taking a sample of $10^4$ points over 4 ms on each channel then I calculate the RMS.
Using ohms law I calculate the resistance of the cell:

$R_x = R \frac{Ch_1-Ch_2}{Ch_2}$

The applied current is a sine curve of 0.5V with varying frequency between 1, 5, 10, 50 and 100 kHz. It is turned on for about 2-3 seconds during the reading of the two channels.

For each frequency I make 10 measurements and take the mean of those.
These measurements are then repeated every 30 min. Shown in the graphs below.

(Sample 1-3: I changed the water and repeated the measurement to see if it's caused by some residue in the cell from previous measurements, although I cleaned it thoroughly)

Why do the curves look like this?
If it's caused by polarization of the ions in the solution wouldn't the resistance increase with time?
I would be happy if someone could point me in the right direction finding a theory explaining this.


texts: Sketching lattice points, primitive axes, primitive cell, and basis of atoms

texts:
I am currently studying Introduction to Solid State Physics, 8th edition, by Kittel. Chapter 1 provides the following figure and accompanying explanations:

It also says the following:

An ideal crystal is constructed by the infinite repetition of identical groups of atoms. A group is called the basis. The set of mathematical points to which the basis is attached is called the lattice. The lattice in three dimensions may be defined by three translation vectors $\mathbf{a}_1$, $\mathbf{a}_2$, $\mathbf{a}_3$, such that the arrangement of atoms in the crystal looks the same when viewed from the point $\mathbf{r}$ as when viewed from every point $\mathbf{r}^\prime$ translated by an integral multiple of the $\mathbf{a}$'s:
$$\mathbf{r}^\prime = \mathbf{r} + u_1 \mathbf{a}_1 + u_2 \mathbf{a}_2 + u_3 \mathbf{a}_3. \tag{1}$$
Here $u_1, u_2, u_3$ are arbitrary integers The set of points $\mathbf{r}^\prime$ defined by (1) for all $u_1, u_2, u_3$ defines the lattice.
The lattice is said to be primitive if any two points from which the atomic arrangement looks the same always satisfy (1) with a suitable choice of the integers $u_1$.

Here are some lattice points I drew:

It doesn't seem to me that any of these lattice points are primitive; that is, I don't think that any of these lattice points satisfy $\mathbf{r}^\prime = \mathbf{r} + u_1 \mathbf{a}_1 + u_2 \mathbf{a}_2 + u_3\mathbf{a}_3$. The irregular pattern present in this space lattice makes it difficult to see how this could be done.
So, in order to satisfy figure 3c, what are the lattice points of interest?
I would greatly appreciate it if people would please take the time to explain this.
EDIT


texts: TLC: Why is a more polar eluent more effective at displacing the points?

texts: If the points are non-polar, I don't see how making the eluent more polar will make them travel faster. Anybody care to explain?


texts: Why do NaHCO₃ and KHCO₃ have different crystal structures?

texts:
Why do $\ce{NaHCO3}$ and $\ce{KHCO3}$ have different crystal structures?

We had this in a test today and this got me stumped...

My questions are:

Do $\ce{NaHCO3}$ and $\ce{KHCO3}$ possess crystal structures?
If they do, why should they have different crystal structures, because they are in the same group and must possess almost similar physical properties.


texts: Acyl chlorides addition-elimination reactions bond forming and bond breaking

texts:
I've recently read up on Acyl chlorides and the addition-elimination reactions that they can react with. However many questions popped up in my head from reading up on this.

During the elimination phase, what determines what bond is eliminated ?

I had in mind that this could have something to do with the bond enthalpies of the bonds bonded to the carbon however when I looked up the bond enthalpies it showed that the bonds with higher bond enthalpy were eliminated rather than the bonds with lower bond enthalpies, how does this make sense?

During the addition stage, why does the pi bond within the carbonyl group open up rather than another bond getting eliminated straight up?

I understand carbon can only have 4 bonds so that's why a bond must open but why does the double bond open? I had in mind electron repulsion from the nucleophile causing the bond to overcome(but this doesn't make sense).

Thank you and please help this make more sense!


texts: Is an imine considered a secondary amine?

texts:
I am looking at the difference between primary, secondary, and tertiary amines.

What about if the nitrogen is double bonded to a carbon?

Is this carbon counted twice, and is the molecule above a considered tertiary amine?


texts: Is it correct to say that H2SO4 is an acid in this reaction?

texts:
Is it correct to say that $\ce{H2SO_4}$ acts as an acid in the following reaction?

$\ce{2Ag + H2SO_4} \rightarrow \ce{Ag_2SO_4 + 2H_2O + SO_2}$

I know it acts as an oxidizing agent, but is it correct to say it shows acidic properties?


texts:
A solution with $\mathrm{pH}=4$ is mixed with a solution with $\mathrm{pH}=10$ in equal volumes. Calculate resultant $\mathrm{pH}$.
  Please note both solution consists of strong acids and/or bases i.e. They will completely dissociate.

$Method 1:$

Let volume be 1L of each

pH of solution 1=4

Concentration of H is $10^{-4} $

pH of solution 2=10

Concentration of H is $10^{-10} $

Resultant concentration =$\frac{10^{-4} +10^{-10} }{2}$

Therefore calculting pH we get 4.301

$Method 2:$

pH of solution 1=4

Concentration of H is $10^{-4} $

pH of solution 2=10

pOH=14-10=4

Concentration of OH=$10^{-4} $

Hence the H and OH neutralizes each other so it will result in neutral solution ph=7

Edit:
I found another method which is kind of same as method 2

Method 3

In Solution 1:
pH=4. Concentration of H is $10^{-4} $

Since pOH=14-pH. Hence pOH=10. Therefore concentration of OH=$10^{-10} $

In solution 2

pH=10. Concentration of H is $10^{-10} $

Since pOH=14-pH. Hence pOH=4. Therefore concentration of OH=$10^{-4} $

So the total concentration of H=concentration of OH

Hence neutrilization reaction would occur and resultant pH will be 7

Which method is right and why??


texts: Does molecular oxygen just mean the oxygen molecule? Or could it refer to a certain state of the molecule (eg. gas or aqueous)?


texts:
For example, can $\ce{NaOH}$ ionize ethanol into ethoxide?

My textbook (Organic Chemistry, 6th edition, by M. Loudon and J. Parise, Roberts & Company 2016) suggests yes — it uses it in its mechanism for the intramolecular substitution of 4-bromo-1-butanol in the presence of $\ce{NaOH}$.

But I was taught that $\ce{^-OH}$ could only ionize thiols, not alcohols. After all, if simple $\ce{NaOH}$ can create alkoxides, why would chemists bother to use $\ce{NaH}$?


texts: Why is $\ce{HClO4}$ more acidic than $\ce{HBrO4}$? But $\ce{HCl}$ is less acidic than $\ce{HBr}$? What determines the acidity? Is it the concentration of $\ce{H+}$? If so, how do these trends develop along the halogen group?


texts: On the process of heating a gas at constant pressure

texts:
Calculate the final temperature and the change in internal energy when $\pu{500 J}$ of energy is transferred as heat to $\pu{0.900 mol}$ $\ce{O2(g)}$ at $\pu{298 K}$ and $\pu{1.00 atm}$ at constant pressure. Treat the gas as ideal.

I am trying to understand how to approach this question without simply plugging the numbers into an equation. Can someone please explain their thought process while solving this? For example, does having constant pressure automatically mean there will be a temperature change and if so, why? What about volume? Why do we not need to know the volume for this equation? Basically, I want to understand what's going on conceptually rather than memorize a few rules. Any help would be much appreciated.


texts: Selective nitro reduction of poly nitro compounds

texts:
Is there any way through which I could selectively reduce one $\ce{NO2}$ group from a dinitro- or trinitro- compound to an amine.

I was reading Solomons and Frhyle and it says that m-dinitrobenzene can be selectively reduced by using $\ce{H2S}$ in aqueous or alcoholic ammonia. It also says that when it is carried out with 2,4-dinitrotoluene it leads to reduction of the 4-nitro group.

So, is there any way to predict which nitro group will be reduced, and/or any mechanism related to this. I have been frantically searching in books and even an internet article would suffice.


texts: What chemicals are in hard wood ash? (Making lye)

texts:
I am trying to make lye or potassium hydroxide. So far I have been leaching ashes in a barrel for a few days. I decided to do some tests on the water to see if it was working. My pH paper said it was basic, so then I reacted it with vinegar to see what would happen. The equation of acetic acid + potassium hydroxide would be this I believe:

$$\ce{KOH + CH3COOH -> CH3COOK + H2O}$$

However, when I mixed the two, it began bubbling after a few seconds. The gas formed smelled like boiled eggs and was white. I assume it is some sulfur compound but I may be wrong. The ashes are mostly from locust wood. Is there anyway to find out what other chemicals are in the ashes and how to separate the potassium hydroxide out?


texts: Determination of spinel structure by CFSE

texts:
$\ce{CuFe2O4}$ has inverse spinel structure, but $\ce{ZnFe2O4}$ has normal spinel structure. Explain.

I know that normal spinels have a structure like $\ce{(A^{II})^{tet}(B^{III})^{oct}_2O_4}$-like structure, while inverse spinels have a $\ce{(B^{III})^{tet}(A^{II}B^{III})^{oct}O4}$-like structure.
Also, I know that if $\ce{B^{III}}$ ion has greater CFSE gain in octahedral site than that of $\ce{A^{II}}$ ion, a normal spinel structure is expected. If $\ce{A^{II}}$ ion has greater CFSE gain in octahedral geometry than the trivalent $\ce{B^{III}}$ ion, then we get an inverse spinel structure.
For the given question, $\ce{Fe}$ has a $\mathrm{3d^6}$ configuration having a structure $\mathrm{t_{2g}^4 e_{g}^2},$ giving a CFSE
$$2(0.6 \Delta_\mathrm{o}) + 4(-0.4 \Delta_\mathrm{o}) = -0.4 \Delta_\mathrm{o},$$
while $\ce{Zn}$ has a $\mathrm{3d^{10}}$ structure having 0 CFSE. So, CFSE of $\ce{Zn}$ is greater than CFSE of $\ce{Fe}.$ So, according to the rule stated before, it gives me an inverse spinel structure.
Similarly for $\ce{Cu},$ it should have a $\mathrm{3d^9}$ $(\mathrm{t_{2g}^6 e_g^3})$ structure which gives a CFSE of
$$3(0.6 \Delta_\mathrm{o}) + 6(-0.4 \Delta_\mathrm{o}) = -0.6 \Delta_\mathrm{o} < -0.4 \Delta_\mathrm{o},$$
which gives a normal spinel structure.
What is wrong with this calculation so that I'm getting opposite structures to those predicted in the question?


texts:
Say I have acetohydrazide ($\ce{CH3CONHNH2}$).

Is it possible, that when I add an acid, an intramolecular condensation reaction occurs, forming the cyclic compound 3-methyl-1H-diazirine:

Furthermore, in general, the mechanism of such a reaction is nucleophilic substitution, right?


texts: API or database for verifying chemical reactions

texts:
Is there a database or API(rest calls) for verifying chemical equations?
Example, Na + Cl -> NaCl + Loss of energy.
So if I want to verify if there is a loss of energy or gain of energy?
Is there any online portal where I can write a chemical equation like above and verify whether its correct or not?
I know there are lots of paid and open source databases. Would be very much helpful if someone can point to me to top databases or sites.


texts: Why is HSO4- shown as an example of a weak acid instead of HSO4?

texts:
I'm watching some (really awesome) chemistry courses, and I think I have a fairly decent handle on acids and bases (or maybe not, and I'm fooling myself). But the teacher just showed a table of weak/strong acids. $\ce{HSO4-}$  was one of them.

I'm wondering, why hydrogen sulfate ion instead of just hydrogen sulfate? Why is $\ce{HSO4-}$ an acid and $\ce{HSO4}$ apparently isn't? This was the only ion on the table. Or does $\ce{HSO4}$ simply not exist?


texts: Is there a substance that will eat through and completely dissolve carbon but not damage engine cylinder, piston nor rings?

texts:
I'm afraid that when I was instructed to be specific in the title of my post, I kind of said it all... Here is the issue:

I have a 2001 Isuzu Rodeo. It has been going through excessive amounts of oil. No blue smoke, no drips whatsoever.

Through an Isuzu forum I find this is a common problem for model years up to and including mine as oil drain holes for the cylinders that were made in the pistons clog with carbon.

In that the vehicle is a 2001, I can well suspect those little holes are well caked and packed.

Though some folks state that they remove the spark plugs, pour a commercial internal auto engine cleaner called B12 into the cylinders and allow an over-nite soak, other auto-techs state that the only way to clear the drain holes is to tear apart the engine and drill the holes in the pistons out or replace them altogether.

Is there a chemical that will eat away and dissolve the carbon whereas after allowing whatever sufficient soak time is suggested I could then change the oil and have a hope for cleared out ports without damage to the metal engine parts?

Thank-you for your thoughts!


texts:
I am not a chemist but for a university project i am dealing with simulations concerning a potentiostat using a 3-electrode setup.

For example in the book Electrochemical Methods (Bard & Faulkner, Second edition 2001) on page 642 they give this example of a (adder) potentiostat which inputs three different potentials $e_1, e_2$ and $e_3$:

While the working electrode is grounded, point $S$ is on virtual ground and by using Kirchhoff's rule they obtain

$$-i_{ref} = i_1 + i_2 + i_3.$$

By using Ohm's law they rewrite this equation into

$$-e_{ref} = e_1 \cdot \frac{R_{ref}}{R_1} + e_2 \cdot \frac{R_{ref}}{R_2} + e_3 \cdot \frac{R_{ref}}{R_3},$$

with $e_{ref}$ being the potential of the working electrode with respect to the reference electrode.

With all resistors having the same value this can be expressed as

$$-e_{ref} = e_1 + e_2 + e_3$$

They state:

  Thus the circuit maintains the working electrode at a potential equal
  to the weighted sum of the inputs

As far as I understand, the electrode of interest is the working electrode which potential should be varied (with the reference electrode providing a stable reference potential) to study its properties. But from the description above the potential of the working electrode does not change and instead the potential at the reference electrode changes.


texts: Coating applied to plastic (polymer suitable for straws) to repel carbon dioxide to prevent "floating"

texts:
We are four students currently finalizing our last exam-project before our bachelor.

We confirmed our hypothesis that straws floating to the top of your drink is a "problem" from our survey.

Our question here would be: Is there any coating or similar scientific method that can be applied to any suitable plastic material, (for the use of consuming beverage) that can prevent the carbon dioxide from sticking to the plastic material, and thereby lifting it to the surface?


texts: What qualifies to be considered as a lone pair-lone pair repulsion?

texts:
Referring to, NCERT Chemistry Part I, Textbook for Class XI[1].

Here the text puts forward three structures of $\ce{ClF3}$.
My teacher said to me that (b) structure is unstable due to lone pair lone pair repulsion while (a) is the most stable of the given structures as there are minimal lone pair and bond pair repulsions and no lone pair lone pair repulsion.
That got me thinking what actually qualifies as a lone pair lone pair repulsions. Is it when the lone pairs are at an angle equal to or less than the 90° or is it something else?
Reference:
[1]: Chemical Bonding and Molecular Structure. NCERT Chemistry Part I, Textbook for Class XI, First Edition(October 2019 Reprint); Uppal, Shveta, Banerjee, Binoy, Eds.; National Council of Educational Research and Training: New Delhi, India, 2006; pp 113.


texts: Why is the pairing energy not considered when calculating the crystal field splitting energy?

texts:
Consider the low-spin octahedral crystal field splitting diagram for a d4 system.

When we calculate the crystal field splitting energy we simply observe the absorbed color of light and calculate the frequency of a photon required to promote an electron from the t2g to the eg orbitals. Why is the spin pairing energy not considered (PE) in these calculations? If we had a simple d3 system, I would understand why the energy of the photon absorbed is equal to the crystal field splitting energy since we are not dealing with any paired electrons; however, in the case of the d4 system, doesn't "removing" one of the paired electrons actually release energy? Why do we say the energy of the photon absorbed is equal to Δo and not Δo - PE?


texts: Do molecules with axial chirality have "stereogenic units"?

texts:
This question is a follow-up to a recent question on discodermolide stereochemistry that I answered here.  In the course of reading IUPAC's definition of "stereogenic center", I wondered if axially chiral molecules such as BINOL have a "stereogenic unit" according to IUPAC.

The part of IUPAC's definition that may (or may not) apply to BINOL is:

  A chain of four non-coplanar atoms (or rigid groups) in a stable conformation, such that an imaginary or real (restricted) rotation (with a change of sign of the torsion angle) about the central bond leads to a stereoisomer.

Here is the structure of (S)-BINOL:

Does the four-atom chain consisting of the O-bond carbons plus the transannular C-C-bound carbons qualify?  I can't quite work out what is meant by "with a change of sign of the torsion angle" and "stable conformation".  If it does qualify, suppose temperature is increased to the point where spontaneous racemization happens (and suppose that any side reactions or decomposition can be ignored).  Is that chain no longer a stereogenic unit?


texts:
This is going to seem like a rather daft question, but what is the definitive half-live for protactinium-234 (234Pa)?  I'm seeing lots of different answers in various academic papers etc.

For instance, in Bonotto & Andrews (2000) the half-life of protactinium-234 (234Pa) is given as 1.18 minutes, but in Edwards et al. (2003) they report the 234Pa half-life as 6.67 hours.  So which one is it?

Bonotto, D.M. & Andrews, J.N. The transfer of uranium isotopes 234U and 238U to the waters interacting with carbonates from Mendip Hills area (England). Applied Radiation and Isotopes. 52, 965-983. 2000.  DOI: http://dx.doi.org/10.1016/S0969-8043(99)00151-7

Edwards, R.L., Gallup, C.D. & C Uranium-series Dating of Marine and Lacustrine Carbonates.  Reviews in Mineralogy & Geochemistry. 52, 363-406 . 2003. URL: http://www.minsocam.org/msa/rim/Rim52.html


texts: I would like to have a solution with a pentavalent positive ion. I need something that, preferably in water:  $\ce{XY -> X^5+ + Y^5-}$. What can XY be?


texts: Does the emission spectrum for a dye depend on the frequency of light used to excite the dye?

texts:
Take a look at the emission spectrum for an arbitrary fluorescent dye: http://en.wikipedia.org/wiki/File:Fluorescein_spectra.jpg

Does the emission spectrum depend on exciting the dye at its peak absorbance wavelength $\lambda_{max}$?  Consider that there is going to be a spread of eigenstates around a particular excited state (http://www.olympusmicro.com/primer/java/jablonski/jabintro/jablonskijavafigure1.jpg), corresponding to particular molecular vibration or rotational modes.

The thought is that, if we excite a dye at a wavelength slightly red-shifted with respect to $\lambda_{max}$, or slightly blue-shifted with respect to $\lambda_{max}$, we'd start out at a different eigenstate clustered around the same excited state (say $S_1$).  I imagine there's a probability of decaying from each of these eigenstates in $S_1$, which gives us the spread for the emission spectrum, so if we bias the initial eigenstate, we'd achieve a different emission spectrum (presumably "statistically" red-shifted with respect to the excitation frequency).  Or is the fluorophore taking a rapid random walk through all accessible eigenstates belonging to a particular excited state?

I suppose we could also ask a similar question with respect to the photoelectric effect in terms of the energy provided to the excited electron (conditioned on having a threshold frequency to span a band gap).


texts: How prevalent is the use of old style names for ions (e.g. ferric, ferrous) outside the classroom

texts: In teaching my preparatory chemistry courses, I'm constantly wondering whether or not I should be having students memorize the "old names" of common multivalent monatomic cations, such as plumbic for lead (IV), plumbous for lead (II), etc.  Every year I teach the course, this information seems increasingly outdated, as I find that I'm coming across these less and less in my general reading.  To the readers I'd like to pose this question: In your practical experience, particularly in industry or other fields outside chemistry, do you still employ this style of referring to ions and compounds?


texts: Configuration of chiral center in cocaine

texts: I couldn't get the absolute configuration for the chiral center I marked. I got R, but according to my answer key it is apparently S. Would really appreciate an explanation.


texts: If stirring negatively affects crystal purity, why is it so?

texts:
My Intellectual Expectations
Intuitively, I would expect strong stirring to improve crystal purity during the process of crystalization. My rationale is that strong stirring would increase contact between each crystal and the variety of ions present in solution at each given level of solubility, and thus minimize the gap between reality and the equilibrium that would be reached if the conditions at each instant (solvent volume and temperature) would be kept equal for a very long time.
Information I have Read
I've read that as a general rule, the size of the crystals that form correlates well with the purity inside the crystals (i.e. that crystal
size in general is a good indicator of purity).
My Conflicting Observations
My observations are that under strong stirring the crystals that form are much smaller than if the crystalization is carried out in still water (at equal rate of cooling / solvent evaporation). This indicates that either crystal size is not a great indicator of purity, or that my rationale is wrong and by counterintuitive mechanisms which I ignore, crystals of greater purity would be formed without stirring.
My Question
Does anyone know 1) Wether stirring the solution during the crystalization  process positively or negatively affects crystal purity? 2) What is the physical explanation of the answer?


texts: Why is active mass of a pure solid or liquid always taken as unity?

texts:
Active mass is defined as the molar concentration ie. number of Gram-moles per litre.

My book then wrote

  Active mass of pure solid/liquid is always 1 .

The book reasoned that

  Molar concentration is directly proportional to density. Since density of solid or liquid always remains constant, the active mass is taken as 1 .

Really? Doesn't the density of the solid reactant decrease when the forward reaction is about to reach the equilibrium??

In a word, I am greatly confused. What is the reason for taking the active mass 1 ? Please help.


texts: How was Mendeleev able to develop his table?

texts:
I asked my general chem instructor this and he didn't know:

Mendeleev was able to group elements and discovered a bunch of them and put them in the correct order in the mid-1800s.  What equipment did he use to do this?  Was he just weighing stuff and guessing?

Specifically, how did he figure out atomic weight?


texts:
Can you explain simply what are the degrees of freedom in chemistry? I don't fathom it very intuitively from Wikipedia.

I have almost no background in physics. I understand that it refers to all the variables that can describe a system, e.g. when talking about the motion of the molecule, the degrees of freedom refer to the ways in which the molecule can move. I understand that an atom can only have translational motion, whereas a molecule can rotate, vibrate and translate. But how this gives the molecule more "freedom" is beyond me.


texts: What is the difference in the reducing power of various ionic hydrides?

texts:
By definition "Ionic or saline hydrides are composed of hydride bound to an electropositive metal, generally an alkali metal or alkaline earth metal."

What is the relative order of reactivities of all the ionic hydrides of alkali and alkaline earth metals?Is there any general trend?
Is the reactivity of alkali/alkaline-earth metal hydrides greater than $\ce{LiAlH4}$ ?
Is the reactivity of alkali/alkaline-earth metal hydrides greater than $\ce{NaBH4}$ ?

I know reducing nature of $\ce{LiAlH4}$>$\ce{NaBH4}$.


texts: What is the relation between volume strength and normality of H2O2?

texts:
I have been told that:
$$\text{equivalent weight of }\ce{H2O2} =\text{molecular weight of }  \ce{H2O2}$$
as it's $n$-factor is $1$ (from balanced equation).
But in my book it's given that:

Molarity $= \frac {V }{11.2}$
Normality $= \frac {V} {5.6}$

Why are they different if equivalent and molecular weights are equal?


texts: Why isn't pure ortho hydrogen possible to obtain?

texts: In school, I've learned that we can only get an ortho hydrogen content upto 75%. Why is that we can obtain a pure sample of para hydrogen, but not ortho hydrogen? What prevents us from isolating ortho hydrogen?


texts: Identity of a green substance formed during electrolysis reaction?

texts:
I did a short experiment in which I connected a $1.5\:\mathrm{V}$ battery with 2 paper clips into a bowl of water to which I added salt. After a while, I saw a yellowish-greenish cloud inside the water around one of the paper clips, and when I took it out, the part that was in the water was more black than the rest of the paper clip. After a while, some of it turned into a greenish color.
What caused the paper clip to change its color?


texts: Negative Pressures in Van der Waals Equation of State

texts:
This is the plot of the Van der Waals equations:

As you can see, the Van der Waals equation predicts a "stretched liquid" area (MNS). Is this physically feasible and what exactly happens there? Are there any intuitive explanations for this?


texts: Does Henry's law depend on curvature of gas/liquid interface?

texts: Could you tell me Henry's law depends on curvature of gas/liquid interface or not? It would be better with references.


texts: Energy of hydrogen bonds vs. kinetic energy of water molecules

texts: I watched an extremely engaging video "Why does ice float in water?" by George Zaidan and Charles Morton, https://www.youtube.com/watch?v=UukRgqzk-KE. In particular, video says "Below 4oC kinetic energy of water molecules falls below the energy of hydrogen bonds. So hydrogen bonds form much more frequently then they break". I decided to verify this statement, and on my way to do so I found energy of hydrogen bonds: "6-30 kJ/mol" according to this source http://book.bionumbers.org/what-is-the-energy-of-a-hydrogen-bond/. However I was unable to find a way to calculate kinetic energy of water molecules. Your help on this matter would be highly appreciated.


texts: Why potential energy is neglected in this problem for calculating the energy difference between two stationary Bohr Orbits?

texts:
Question
An electron in a hydrogen like atom makes a transition from a state in which its de-Broglie wavelength is $\lambda_1$ to a state in which its de-Broglie wavelength is $\lambda_2$, then wavelength of photon generated due to this transition will be ___________.

The solution for this problem as given in my book is as follows:

In the first step, it is given that the energy difference is just equal to the kinetic energy difference. How is this possible? Why have they neglected the potential energy in calculating the energy difference since the two stationary orbits in Bohr's model have different potential as well as kinetic energies.
Please clarify my doubt.


texts: What is exactly ortho effect in Reimmer-Timmer reaction?

texts: In the Reimmer-Timmer reaction cho group is added to only at ortho position not at para position , I got the answer for this as ortho effect. So what is exactly ortho effect.


texts: How to go about deciding the acidic strength of a functional group in an aromatic compound?

texts: The question requires me to identify the decreasing order of the acidic strength of the following functional group. But I'm afraid I don't know how to distinguish one from the other since all the hydroxyl groups would be in resonance. What would be the next step in this case? I felt like the answer should start with (i) as there is a carbonyl carbon near and the delocalisation would be stabilised.


texts: Is food that burnt in an 18/10 stainless steel pot still edible?

texts: I was cooking Christmas tamales in an 18/10 stainless steel pot and I accidentally let the water evaporate and the pot started burning.  I think it was probably burning for around 5 minutes or less.  There were a lot of tamales in there and I'm wondering if they are safe to eat or if I have to throw them out?


texts: Coordinates for molecules except cartesian and zmatrix

texts:
Every program in theoretical chemistry that I know uses different ways of writing their input. The same holds true for writing the geometry of the molecules of interest. But they can all be reduced to be either cartesian or zmatrix representation.
Intuitively these two are the natural answers to the problem of specifying a molecule geometry.

Nevertheless:
Are there programs in use that use anything different e.g. zylindrical, or elliptical coordinates?


texts: Product of the reaction between chalcone and sodium methoxide in methanol

texts:
I'm a bit lost on how to do this, for Product C I can see two things happening:

1) The $\ce{-OCH3}$ attacks the alpha hydrogen, but that doesn't really make sense as then you would get two double bonds next to one another

2) The $\ce{-OCH3}$ attacks the electrophilic carbon, but then we know the negatively charged oxygen cannot collapse back because then the $\ce{-OCH3}$ would leave. So, would it just get printed by $\ce{HOCH3}?$ And if it does that how would it react with the second set of reactions?


texts: What is the reaction between piperine and concentrated sulfuric acid?

texts:
Piperine was chemically characterized by reaction with acids. This was done by dropping concentrated $\ce{HNO3},$ $\ce{HCl},$ and $\ce{H2SO4}$ to a sample of piperine. Both $\ce{HNO3}$ and $\ce{HCl}$ produced yellow solutions while sulfuric acid produced a blood-red solution.

What happens to piperine as it reacted with $\ce{H2SO4}$ and why it turned blood-red? Also, what is the difference of that reaction with the reaction of piperine with $\ce{HNO3}$ and $\ce{HCl}?$

Edit: Late addition for viewer's convenience:

The piperine structure is shown below:


texts:
This is a question I have for Chemistry homework, but I don't understand how to solve it without a given mass. I narrowed the choices down (see below _) I know a limiting reactant well limits the reaction (so if there are 2 reactants) and the react left is the excess reactant.

I thought Propane would be the limiting reactant because the oxygen is in excess (though that was incorrect).

Then, I though Oxygen would be the limiting reactant (naturally) since its a combustion reaction (though that is incorrect).

Determine whether each reaction depends on a limiting reactant. Explain why or why not and identify the limiting reactant. (Select all that apply.)

(c) Propane (C3H8) burns in excess oxygen to produce carbon dioxide and water.

Yes, one reactant is naturally limiting.
Yes, there are two reactants.
No, all reactants are in excess.
No, there is only one reactant.
propane
oxygen
carbon dioxide
water
Not enough information to identify which is the limiting reactant.

Yes, one reactant is naturally limiting.
Yes, there are two reactants.
No, all reactants are in excess.
propane
oxygen
Not enough information to identify which is the limiting reactant.


texts: Why do laws of thermodynamics "outweigh" any other law ever formulated?

texts:
"It is the only physical theory of universal content concerning which I am convinced that within the framework of the applicability of its basic concepts, it will never be overthrown." - Albert Einstein
"Nothing in life is certain except death, taxes and the second law of thermodynamics". - Seth Lloyd
“If someone points out to you that your pet theory of the universe is in disagreement with Maxwell’s equations — then so much the worse for Maxwell's equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation." - Arthur Eddington
"“Every question or effect has the right to exist if it does not contradict the second law of thermodynamics”. - Boris Pavlovich
“A good many times I have been present at gatherings of people who, by the standards of the traditional culture, are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the second law of thermodynamics. The response was cold: it was also negative. Yet I was asking something which is the scientific equivalent of: Have you read a work of Shakespeare's?” - C.P. Snow

I find these particularly interesting but there are many others which mark the supremacy of the laws of thermodynamics over any other law ever formulated by man.
I have just begun to learn the laws of thermodynamics and it is indeed very different and "interesting" but so was Newton's laws of motion, Faraday's laws, Heisenberg's uncertainty principle, Einstein's theory of relativity, then why are laws of thermodynamics considered so immutable and supreme to other laws. What is it that makes all these great people hold them as so impactful and perpetual and makes these laws outweigh others?


texts:
Recently, I have been reading the Nobel Lecture given by Kenichi Fukui when he won the Nobel Prize in 1981, for his contributions to the development of Frontier Molecular Orbital Theory. One of the most well-known ideas in this theory is that principally, the reactivity of molecules can be understood by looking at their HOMOs and LUMOs. On p. 15 of the lecture notes, it is written:

  If HOMO or LUMO happens to be inadequate owing to its extension, the
  symmetry, or the nodal property, the next orbital should be sought for. One of
  the simplest examples of such an instance is the protonation of pyridine. In this case, the nitrogen lone-pair orbital is not HOMO, but the addition of proton to the nitrogen lone-pair so as not to disturb the π conjugation will evidently be more advantageous than the addition to higher occupied π orbitals which may intercept the π conjugation. Thus, the reason why proton dare not add to the positions of large amplitude of π HOMO in this case will easily be understood. It is not completely satisfactory to dispose of a disagreement between the HOMO-LUMO argument and the experimental fact formally as an exception to the theory. A so-called exception does possess its own reason. To investigate what the reason is will possibly yield a novel finding.

In the above paragraph, Fukui is essentially telling us that consideration of the HOMO of the pyridine molecule would not allow us to determine the site of protonation. As Fukui writes, the HOMO of this molecule is one of $\pi$ MOs of the aromatic system while in this protonation reaction, the lone pair orbital on the nitrogen atom reacts. He also ends off by saying that further investigation of this example may "possibly yield a novel finding".

Firstly, I would like to ask if any further investigation has been done into this and whether any novel finding has been derived to date? Secondly, I would like to put forth my own rationalisation of this phenomenon. Personally, I do not think that this example poses as an exception to the theory because this acid-base phenomenon is controlled by thermodynamics. That is to say, whether the protonation occurs, it should result in the resultant conjugate acid being of the greatest stability (i.e. Gibbs free energies need to be considered). Thus, kinetic factors, like orbital interactions between frontier orbitals, become much less relevant. Would you agree with my rationalisation?


texts:
The question is(See image):

I know that initially a cyanohydrin will be formed. On reaction with $\ce{H2SO4}$, the cyanohydrin will give a carboxylic acid/an amide.

Here's my doubt:

Since the medium is highly concentrated acid medium(95% $\ce {H2SO4}$), the quantity of water in the medium is less, which means lesser of the nucleophile(water in this case). Hence the cyanohydrin should undergo partial hydrolysis to give an amide(because of lesser water!).  Therefore, according to me the answer should be (D).(Had it been dilute acid medium I would have gone with the carboxylic acid product.) However, in this case my answer is not correct...:(

What is incorrect about my thinking?


texts: Are lustre and conductivity directly related?

texts:
In a question that I had asked before, Is chromium the shiniest metal?, I received the answer that silver was, in fact the most lustrous metal for visible wavelengths. At the same time, silver is also the best metallic conductor, having a resistivity of $1.59×10^{-8}$. I know that lustre of metals was explained by considering the oscillations of free electrons in them, so, I could hypothesize that silver allows the electrons to move around better than other metals, allowing to shine and conduct more. As a comparison, the pictures of polished silver, aluminum and iron are shown below.

Silver: ($\rho =1.59×10^{-8}$)

Aluminum: ($\rho =2.65×10^{-8}$)

Iron: ($\rho =9.71×10^{-8}$)

Can I safely conclude that conductivity and lustre are directly related?


texts: Which process is used to separate Hydrogen and Oxygen from Water?

texts: What's the process called where you can use electricity to separate the oxygen and hydrogen from  water? Is it electrolysis? Can it be applied to other liquids?


texts: Band gap difference in different allotropes of Group4 materials

texts: Diamond and bulk Si are both Group 4 elements found in their $sp^3$ hybridized states, having bandgaps of around 5.3eV and 1.1eV respectively, but Graphene and Silicene are both $sp^2$ hybridized allotropes of the said elements and are zero bandgap materials. What promotes this change in behaviour? Is it the change in hybridization? or the super-aromaticity??


texts: Given a theoretical combustion engine, how can I calculate the output of this engine depending on the fuel it uses?

texts:
I'm writing a Minecraft mod (for those who don't know, it's sort of like a smaller "program" that loads into the Minecraft game and expands it, by adding other things to it).

My question is: consider a combustion engine that runs on anything that is flammable (even though Uranium has a lot of chemical energy, it can't be set on fire, so it's out).

The engine can burn, for instance, acetone, methane, ethanol, methanol, etc.

By burning these fuels the energy converts their chemical energy into mechanical or kinetic engine to move it's gears, pistons and stuff (whatever the engine uses to transmite the energy).

What is the simplest way of comming up with a "good enough approximation" function

energy = f(fuel)

What goes in this function? the volume of the engine doesn't change, so not that. pressure certainly is a factor (maybe the answer itself?) does it have anything to do with the Ideal Gas Law? What about the density of the fuel, molar mass, specific heat, etc?


texts: Freezing all the water on earth with a seed crystal

texts:
I was recently reading the satirical, fictional book Cat's Cradle by Kurt Vonnegut. In this book, one of the major subplots is the invention of a mythical polymorph of ice called ice-9 in the book. In the book, it is described that if this polymorph of ice were to touch actual water, all the water, inevitably touching through oceans, rivers, lakes, etc. would freeze into this polymorph of ice which is purported to melt at a temperature over 100 degrees Fahrenheit.

This raises two questions for me:

First, would something like this actually happen? I know, for instance, a method people use for purifying crystals is to create a supersaturated solution and disturb the substance and it will crystallize quite dramatically. Could something similar happen here in the sense that the mythical ice-9 structure would be introduced into liquid water (which to ice-9 is a supersaturated solution of water) and create a massive crystal out of all water?

Second, and more in reality, is there any solid that is like this? A solid which has two stable crystal structure that exist at temperature reachable in everyday life at about atmospheric pressure? And if so, can you actually convert one crystal structure to another easily? And would one of the liquids behave as a supersaturated solution of the crystal?

Sorry if that is a little unclear. I am sincerely interested in this and can clarify if there is any confusion.

Anything interesting along those lines would be considered relevant in my mind.


texts:
I'm looking at redox half-reactions, such as the one below:
$$\ce{Zn(s) -> Zn^2+(aq) + 2 e-}$$
Does the zinc react with the water and dissociate into ions? Why doesn't solid zinc have a charge?


texts: What i know about the above question is that a compound acts as an oxidising as well as reducing agent when the oxidation of central metal is somewhere between it's maximum and minimum oxidation state which is in the case for $NaNO_2,NaNO$.I don't know how to choose between the two.Any more information about the behaviour of other two compounds will be helpful.Thank you


texts: Why is the electronic configuration of gold written in this order?

texts:
This is an example from my chem text.

  Eletronic configuration for $\ce{^79Au}$:
  $$\ce{1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 \color{red}{4f^14} 5d^10 \color{red}{6s^1}}$$
  (Emphasis mine)

If I would follow the Linus Pauling diagram, I might write it as "$\ce{5p^6 6s^1 4f^14}$" rather than the example above. Why does the $\ce{6s^1}$ jump to the last position in the line?


texts:
My book says that:

Oxides in higher oxidation states of elements of group 14 are generally more acidic than those in lower oxidation states.The dioxides $\ce{CO2}$, $\ce{SiO2}$ and $\ce{GeO2}$ are acidic whereas $\ce{SnO2}$ and $\ce{PbO2}$ are amphoteric in nature. Among monoxides, $\ce{CO}$ is neutral, $\ce{GeO}$ is distinctly acidic whereas $\ce{SnO}$ and $\ce{PbO}$ are amphoteric.

First and foremost:
How can an oxide be acidic? Is it because of their reactions with other compounds? I know about Arrhenius, Lewis and Bronsted acids and bases but still can't seem to connect!

Secondly, why does the book say "Oxides in higher oxidation states of elements of group 14 are generally more acidic than those in lower oxidation states"?  Is there a logical reason behind this?

Is the trend mentioned in the second question followed by all groups of the periodic table and not just for group 14?
By 'all groups', I am referring to s and p block elements. I don't know much about the chemistry of the d and f block elements - I will study them in a few weeks time, but I reckon they should also follow this trend.


texts: Mechanism of Hypervalent Iodine Phenolic Coupling

texts:
I need some help understanding the hypervalent iodine phenolic coupling reaction taking place in this synthesis of morphine, the reaction uses $\ce{PhI(OAc)2}$ as the hypervalent reagent and trifluoroethanol as a solvent.

What is the mechanism taking place here? From my understanding the hypervalent compound contains a 3c-4e bond in which the iodide bears the positive charge and therefore is what the lone pair on the $\ce{-OH}$ attacks, what takes place after this?

This reaction results in the dearomatisation of one of the phenol rings, isn't a dearomatised ring a thermodynamically more unstable product, what is driving this reaction?

The paper describes the trifluoroethanol solvent as crucial, what makes the use of this solvent crucial? Is it the lack of nucleophilicity preventing a reaction with the iodine reagent?

The paper I am looking at is this one for reference.


texts:
Is it true that the sea water is composed of about $86\%$ oxygen, $11\%$ hydrogen and $3\%$ of minerals? The chemical formula of water is $\ce{H2O}$ (two hydrogen and one oxgen) that shows that the number of hydrogen is greater than that of oxygen.

If the number of hydrogen is greater, then why does the sea water consist of $11\%$ hydrogen and $86\%$ oxygen, which is lesser than the oxygen?

The book which I am reading says which is confusing me:

  ... Seawater is composed of about $86\%$ oxygen, $11\%$ hydrogen and $3\%$ of minerals, consisting mainly of sodium and chlorine.


texts:
"Burned food is bad for you." This basic tennet appears to be firmly held by specialists.

Hence burnt food should be carefully cleaned from pots before subsequent use, and likewise on grilling equipment.

Yet the standard care for cast-iron cookware involves coating with a thin layer of oil and heating. The desirable temperature is variously indicated to be between 250F and 400F, possibly depending on the type of oil. The temperature for this reaction, polymerization, is just short of carbonization.

What is the stability of polymerized oil? Is it established whether it is soluble during subsequent cooking with new oil?

Previous relevant question(s):

Molecular structure


texts:
I am using a rotary evaporator to separate DCM (dichloromethane) from some nasty tars.
Before the evaporation is completed, I stop the process and collect the remaining slurry.
The slurry is then positioned in a constant temperature oven, for a secondary evaporation. After cooling in a desiccator, the tar is measured.

The problem is that some of the tars remain deposited on the flask's wall. I can easily remove them with a soft brush, however this is a problem for 2 reasons:

Some of the tar is lost, retained on the brush itself ( I require a very high precision since I work with samples of 100 or so mg)
The amount of DCM for secondary evaporation is increased (I am trying to reduce that amount as much as possible)

Is there a round bottomed flask that has a TEFLON like coating on the inside, that can prevent the tar deposition on the walls?

There seem to be a lot of products that are referred as " Flask with Plastic Safety Coating". On which side is the coating applied (I assume is the outside)


texts: How do acids help 'solubilise' compounds?

texts:
I've heard that root hair cells in plants secrete acids to help 'solubilise minerals' so that they dissociate and are in ion form... this supposedly allows them to be absorbed.

How so can acids solubilise certain compounds? It must be noted: I am a student and my solubility knowledge is fairly basic. I understand that ionic compounds dissolve in water because of the water molecule and the compound's polarity, but it goes no further than that.

Thank you in advance.


texts: How does solubility of corrosion product affects rate of corrosion?

texts: Why is it that if the corrosion product are soluble, then the rate of corrosion increases while insoluble corrosion products cause rate of corrosion to decrease?(How exactly would insoluble corrosion product protect the material?)


texts: How to evaluate the heat of formation with computational chemistry?

texts:
I'm sorry if this is a stupid question, but since I'm a beginner with computational chemistry, please, be patient.

Let's consider the reaction of formation of water:

$$\ce{1/2 O2(g) + H2(g) -> H2O(g)}$$

This reaction shoud give a $\Delta_\mathrm fH^\circ = -241.83~\mathrm{kJ/mol}$. The reaction is intentionally simple to let me run fast calculations and tests with single point energies.

First, I've performed a geometry optimization on $\ce{H2O}$, $\ce{O2}$ and $\ce{H2}$ (HF/6-31G*). Then, I've used M06/Def2-QZVPP for the single points:

$E_\mathrm{SP}(\ce{H2O}) = -76.431519932791~E_\mathrm h$
$E_\mathrm{SP}(\ce{O2}) = -150.262365177069~E_\mathrm h$
$E_\mathrm{SP}(\ce{H2}) = -1.171819656537~E_\mathrm h$

In this case, doing $$E_\mathrm{SP}(\ce{H2O}) - \left(\frac12 E_\mathrm{SP}(\ce{O2}) + E_\mathrm{SP}(\ce{H2})\right) = \Delta E$$ I'm getting $\Delta E = -0.1285176877195084~E_\mathrm h$ that is equal to $-337.42312874~\mathrm{kJ/mol}$, almost $96.6~\mathrm{kJ/mol}$ higher than the reference of $-241.83~\mathrm{kJ/mol}$.
Is this the correct approach for a case like this? Or is this discrepancy normal?


texts: What is the range of photon energies can be effectively used to split a diatomic molecule like hydrogen?

texts:
I saw photo-ignition of hydrogen-chlorine mixture using UV light on YouTube.

Chlorine molecule bond dissociation energy is $\pu{2.51 eV}$ (bluish colour).
Bromine molecule bond dissociation energy is $\pu{2 eV}$ (orange colour).

Can I use any photon which has energies greater than $\pu{2 eV}$ to split bromine molecule,  like green or blue or UV light? Or should I use only photons which has energies around $\pu{2 eV}$?

My concern is about absorption spectrum of gases. And this question is not just for bromine gas, but for any diatomic molecule like hydrogen or Chlorine.


texts: Micelles absorb fat, is there an adjective for this?

texts:
"Hygroscopic" means the capacity to absorb water. Is there an adjective to describe the same idea except for the absorption of lipids? Like, when you wash your hands with soap and the soap micelles absorb the bacon grease, for example.

I'd like to say that micelles have ____lipid-absorbing_____ properties.


texts:
I was given $4$  gases, which gases had the same temperature ,pressure and mass and was told to determine the gas with the greatest volume.

The gases were $\ce{CH4}$, $\ce{NO}$, $\ce{C2H2}$ and $\ce{CO2}$.

So I assumed the mass was $1$ gram and used the formula $n=\frac{\text{mass}}{\text{molar mass}}$  and found that $\ce{NO}$ had the greatest volume but the correct answer given to me was $\ce{CH4}$.

I cannot find out where I went wrong?


texts:
From what I understand CO2 drycleaning is essentially heating and pressurizing Co2 until it is at a supercritical state and then using it as a solvent to wash clothing. I just don't understand why clothing that comes out of the resulting process would be cold. Doesn't supercritical carbon dioxide require temperatures of at least ~300 Kelvin to form? Anyway, I would greatly appreciate it if someone with more knowledge on the subject could provide a basic outline as to how CO2 dry-cleaning works. There are very few resources that go into detail on the process.

Thanks!


texts: Why does magnesium oxide not react with water?

texts:
There is a question in my textbook which asks "which of the reactions are not possible to occur". The right answer is $\ce{MgO + H2O}$ and my chemistry teacher confirmed it. Why is that so? I thought that it would form $\ce{Mg(OH)2}$.

Does the reactivity also depend on the temperature?


texts: How to calculate the percentage yield for enantiomers in free radical halogenation?

texts:
How many mono-chlorinated products of 2-methyl butane will be formed upon chlorination in the presence of sunlight?
  Find the percentage of major product formed.

Six products were formed: two pairs of enantiomers and two achiral chloroalkanes.

Until here my answer was correct, confirmed by my teacher.

For the second part that is the percentage yield I had an issue with the enantiomers. I calculated the relative yield ratios by multiplying probability factor and rate factor.

For cases A and B, where enantiomers are being formed, I further multiplied $p_\mathrm{f} \times r_\mathrm{f}$ by half since there's an equal likelihood of each of the enantiomers to form. My teacher said this is wrong, as we do not multiply it by half.

So, my question is why?


texts: Is it harmful to mix Hydrogen Peroxide with oven cleaning spray?

texts: My mother recently stumbled upon this mix when she was trying to remove stains from some laundry. When just the peroxide didn't work, she sprayed on some Easy Off, and the stain disappeared. Now she uses this method regularly, and I'm worried that it might be toxic or something. I just want to make sure she isn't poisoning herself.


texts:
$1.00~\mathrm{g}$ of water is introduced into a $5.00~\mathrm{L}$ flask at $50~^\circ\mathrm{C}$. What mass of water is present as a liquid when equilibrium is established? Also you know $92.5~\mathrm{mmHg}$ (vapor pressure).

  $0.083~\mathrm{g}$
  $0.41~\mathrm{g}$
  $0.59~\mathrm{g}$
  $0.91~\mathrm{g}$

I need thorough explanation for each step because I'm new to this. This question is in the gases section of the book, so I think I need to apply the ideal gas law, but I don't know.

With the help from the comment I came up with the following solution:

$$
\begin{align}
\frac{92.5}{760}~\mathrm{atm} \cdot 5.00~\mathrm{L} &= n \cdot 0.08206 \cdot 323~\mathrm{K}\\
n &= 0.023~\mathrm{mol}
\end{align}
$$

Since $1~\mathrm{mol}$ of $\ce{H2O}$ is $18~\mathrm{g}$, the answer is $0.414~\mathrm{g}$, or (2) $0.41~\mathrm{g}$.


texts: Why do colligative properties depend only on number of solute particles?

texts: Colligative properties depend solely on the number of even though the interactive forces are different for different solute-solvent pairs. So why is the dependence only on the number of solute?


texts: short/extensive training on computational chemistry

texts: I want to take a training on computational works in chemistry. It should be of a short duration. Where in Europe I can find it?


texts: Reactivity and transport safety of substituted methyl benzoates

texts:
This was a practice question from an MCAT book whose answer I didn't really understand:

The normal reactivity of methyl benzoate is affected by the presence of certain substituents. Which of the following substituents will decrease methyl benzoate reactivity making it safer for transport?
a) $\ce{NO2}$
b) Hydrogen
c) $\ce{Br}$
d) $\ce{CH3}$

They give the answer as (a) because "in order to decrease the reactivity of  benzene molecule, an electron withdrawing deactivating substituent must be used." However, I thought the reactive part of the molecule would be the carboxylic acid, and so I would've expected (d) to decrease the reactivity of the molecule because it's electron donating.
I suppose if the question meant the reactivity of the ring itself, then the answer is (a) since electron withdrawing substituents on a benzene ring lower its reactivity.
So my question is: How would one reasonably infer that the reactive part of this molecule is the benzene ring itself instead of the carboxylic acid?


texts:
I tried to find info on tin toxicity but there is not much.
Wikipedia here says that it is not very poisonous; but there could be cases.

My question is: is it dangerous to say have a coffee boiled in a tin container? I know that coffee has some acidity, so it can probably react with tin.


texts: I would like to detect the electric current going through the water solution using the colour reaction in this water solution. What chemicals can be used for this solution to make it electrochromic.


texts: Is there a relationship between boiling point and van der Waals constants

texts:
Is there a relation of the boiling point of a gas with its van der Waals constants, $a$ & $b$?

I know if constant $a$ is greater, then the boiling point will also be greater, because of more attraction between the molecules, but does the boiling point depend on $b$ too? If two gases have the same $a$ but different $b$, can I tell which of the two gases will have a higher boiling point or nearly same boiling point?


texts: Difference between ionization enthalpy and work function?

texts: The work function is stated as the energy required to eject an electron out.. And ionisation enthalpy is stated energy required to move an electron out of the gaseous atom. I don't understand if there is any difference.


texts: Molar absorption coefficient of H2SO4(aq) for UV-vis spectrophotometry

texts:
I am wondering if there is anything in the literature that can tell me what is the molar absorptivity (i.e. molar extinction coefficient) of aqueous sulfuric acid at a given wavelength (in my case, I am interested in $\lambda_\mathrm{max}(\mathrm{ferroin}) = \pu{508 nm}$).

In addition, is there a good resource in the literature to look up these values for common substances? I haven't yet been able to find anything of the sort.


texts:
It is known that the enol form double bond tends to attack the electrophilic carbon centre in an aldol reaction. But what will be the majour product in this reaction.
The latter one may be enol attack but forming a 5 membered ring. The former apparently is more stable forming a six membered ring but the enol form is less stable having lower no. of hyperconjugating structures(since greater number of hyperconjugation structures directs to more stablity.) So, is the keto form actually involved in aldol in this case, contrary to general mechanism? Moreover what will be the majour product?


texts: Is Geologic Mineral Trapping of Chlorine Plausible?

texts:
One strategy for sequestration of $\ce{CO2}$ is mineral trapping arising from geologic sequestration.  Another strategy is mineral trapping in concrete via the Mineralization via Aqueous Precipitation or MAP process.  In particular, Alkalinity Based on Low Energy or ABLE process offers an energy efficient MAP process.  However the ABLE process produces $\ce{Cl2}$ (or $\ce{HCl}$), which, at scale, produces its own environmental impact.

One way of dealing with $\ce{Cl2}$ (or $\ce{HCl}$) might be mineral trapping via geologic sequestration.

Is this plausible?


texts: Does concentration or pKa define acid strength?

texts:
For example, is 3M HCl a stronger acid than 1M HCl?

I would reason that the concentration of an acid/base does not influence its strength. Strength is determined by the pKa, and, as per Le Chatelier's Principle, the initial concentration does not influence the equilibrium constant.

It may shift the equilibrium concentrations (meaning that the pH is higher for the 3M HCl), but it will not change $K_a=\frac{[H_3O^+][Cl^-]}{[HCl]}$ at equilibrium.

Is this right?


texts: What chemical could dissolve low-density polyethylene?

texts:
What chemical could dissolve plastic aside from acetone? Preferably, low-cost and environmentally friendly. Any suggestions would be helpful.

I'm targeting for thin plastic (low-density polyethylene). Environmentally friendly for me is that it follows the EPA standards from the USA. I'm targeting for around 150 USD. I'm okay with solvents that make the plastic swell, but a chemical that could dissolve it is preferable.


texts:
If I mix sodium fluoride, calcium carbonate powder, and water, under what conditions (if any) would there be an equilibrium?

I.e. assume we start out with fully dissociated $\ce{Na+(aq) + F-(aq)}$, because it's fairly soluble. But when I add the $\ce{CaCO3}$, it's only slightly soluble, so assume an excess of solid $\ce{CaCO3}$ and a small amount dissolved.
Will that be stable with $\ce{NaF}$ concentration much greater than the saturated concentrations of $\ce{CaCO3}$, or will $\ce{CaF2}$ start to precipitate, and will it continue until exhaustion of a reactant, or reach equilibrium?

I'm wondering if it's the relative solubilities of $\ce{CaCO3}$ and $\ce{CaF2}$ that will drive the equilibrium (if that's what it is) one way or the other. I can't work out how to apply the theory of an equilibrium constant because of the excess solid reactant and corresponding possible precipitate messes up how concentrations balance out in a normal equilibrium… And I'm wondering if the absolute concentration of $\ce{NaF}$ effects things as well.

Any pointers appreciated. Or even some jargon to say what this kind of reaction is called.


texts: Why are there only 6 series (Lymen, Balmer, Paschen, Bracket, Pfund and H.Davy) in the hydrogen atomic spectrum? Why can't there be more?

texts:
The Balmer series, for example, is formed when the electron jumps from $n_2 = 3, 4, 5, \ldots, ∞$ to $n_1 = 2.$

The Humphry Davy series (The last series is formed when electron jumps from $n_2 = 7, 8, 9, \ldots, ∞$ to $n_1 = 6.$

Can't there be another series formed when electron jumps from $n_2 = 8,9,10... \ldots, ∞$ to $n_1 = 7?$


texts: Out of KCl, CaCl2, MgCl2, NaCl, which causes the greatest corrosion rate of iron and why?

texts: I know that salts act as an electrolyte in a redox process and rusting of iron, where iron loses electrons and oxidizes, and oxygen gains electrons and reduces. I did an experiment with KCl, NaCl, MgCl2 and CaCl2 salts dissolved in water, then dipped iron nails in the separate solutions to see which nail would rust more over a period of time. My result was MgCl2>CaCl2>KCl>NaCl. For my analysis I'm looking for an explanation as to why MgCl2 solution had the most rust, the CaCl2 the second most ect. I wondered about periodic trends and how I could look at electron affinity to see which salt could accept electrons the easiest, but I'm not sure if it's right. I just want help on this chemical process and an in depth explanation for my results. Thanks!


texts: Reaction mechanism for oxidation of primary alcohol to carboxylic acid

texts:
Can someone help me identify the steps for the following reaction? I'd like to keep track of everything that happens. I can't figure out what happens with oxidation in this context, and thus can't get started.
It's 2-methylpropan-1-ol oxidized with potassium dichromate(VI) in aqueous sulfuric acid to yield 2-methylpropanoic acid (also known as isobutyric acid).


texts: Do carbon monoxide and graphene oxide react?

texts:
I want to know what happens if  $\ce{CO}$ and graphene oxide (GO) react.

Through the internet the reaction of GO with $\ce{H2O}$ is available but I did not find anything about carbon monoxide.


texts: Are atomic mass unit (amu), unified mass unit (u) and Dalton (Da) the same unit but with different names?

texts:
I recently read up on some chemistry and found these units of mass:

atomic mass unit (amu)
unified atomic mass unit (u)
Dalton (Da)

Are they all the same unit but just with different names or are they different? I'm looking for a simple explanation as I'm new to chemistry.


texts: What could be causing my cyclic voltammograms to have a sloped scan?

texts:
I am running a CV (cyclic voltammogram) in a two compartment bulk electrolysis cell with pH 7 phosphate buffer (0.5 ion concentration) and a napheon membrane separating the two compartments. I'm using a platinum microelectrode with a Ag/AgCl psudo reference electrode and a large platinum flag counter electrode. Currently I am running the setup all in one side of the two compartment cell in order to isolate the distance issue.
I took a first order derivative to show the slope of the line is rather constant.

This was a background taken, after degassing with both stirring and helium sparging, using a polished 25 micron platinum microelectrode. Any ideas what could be causing my background scan to be a literal diagonal line, rather than flat like a regular baseline?


texts: Does heating potato starch destroy its resistant starch?

texts:
Resistant starch, as found in potato starch, is supposed to have health benefits. There are differing opinions on whether or not heating potato starch destroys the resistant starch in it and thereby also the supposed health benefits. I would like to know what the scientific consensus is.
That reheating potato starch destroys its resistant starch, is argued by:

Marks Daily Apple

Any idea if heating the potato starch (like using it as a thickening agent in soups/stews) negates its RS function? Yes, the RS will be completely negated.

Diabetes Sister

If potato starch is heated it converts to normal starch and you will get none of the amazing benefits.

Mark Hyman

Resistant starch is made by cooking and then cooling starches like potatoes or rice and not reheating them, transforming regular starch into resistant starch.

Healthline

It’s important to not heat the potato starch. Instead, prepare the meal and then add the potato starch once the dish has cooled.

That reheating potato starch does not destroy its resistant starch, is argued by:

John Hopkins

Reheating doesn’t decrease the amount of resistant starch.

Bernard Preston

Carbs, cooked and then cooled, and again reheated, pass through the small intestine into the colon as resistant starch where they are instead fermented by the healthy probiotic bacteria; instead of forming simple sugars with all the potential problems of obesity, diabetes and glucose intolerance.

Chris Kresser

Each heating and cooling cycle adds more resistant starch.

There also appear to be different types of resistant starches, which might complicate the discussion in ways I do not know.


texts: Reaction between silver nitrate and aluminum chloride

texts:
I googled a bit about what $\ce{AgNO3 + AlCl3}$ will yield and found out the following:

$\ce{3AgNO3 + AlCl3 -> Al(NO3)3 + 3AgCl}$

Why is that? I know that $\ce{Ag}$ is higher up in the reactivity series than $\ce{Al}$ but that does not make sense to me in this problem. Is it because $\ce{Cl}$ is just one when $\ce{NO3}$ is multiple?


texts: In Graham's law, is the rate of effusion only dependent on molar mass?

texts:
According to Graham's Law, the effusion rate of a gas is inversely proportional to the square root of the molar mass of the gas.

However, consider this situation: We have s balloon with 1 mole of neon gas and another with 2 moles of neon gas. The gases are in thermal equilibrium and occupy the same volume. In this scenario, would the rate of effusion be the same?

The molar mass of the neon in both balloons is the same, so according to Graham's Law the rates would be the same. But intuitively, thinking about 2 moles versus 1, the pressure is doubled if volume and temperature are kept constant. And if the pressure is doubled, more collisions per second occur, so I would think that despite Graham's Law, the rate of effusion is also affected by the number of moles.


texts:
I'm trying to find an alternative to simple ring stands to hold a simple electrochemical cell.

The issue is that it is difficult to adjust the height to the right position to within even a couple inches. If you try to screw the stand in it can drop or lean, and I need to be able to adjust it to within at least an inch without it falling down.

I use a micrometer to adjust an electrode coming in from the top, and I don't have a lot of play to push down.

It is also not easy to adjust the stand from under a few hood, due to the nature of the screw.

It would also be nice if the clamp could be adjusted along the y-axis to move it closer or farther from the stand for different situations.


texts: Using sodium peroxide to scrub carbon dioxide emissions

texts:
I am a student from a school and recently I came across the reaction

$\ce{2Na2O2 + 2CO2 -> 2Na2CO3 + O2}$

Can't we use this reaction to reduce $\ce{CO2}$ in the atmosphere by placing some $\ce{Na2O2}$ filters in places where there is high level $\ce{CO2}$ emission? I then realized that the filter would have to be loaded with lot of $\ce{Na2O2}$ to achieve this. So why not adsorb as much $\ce{CO2}$ as much as possible using a good adsorbent for $\ce{CO2}$. I am not sure if there are other methods better than these but I would like to know if there is any?


texts: What is the longest systematic name used for a compound that actually exists?

texts:
The answer to this question (Does IUPAC nomenclature have the ability to name all organic compounds?) which references the complex biomolecule Maitotoxin which has a ridiculously long systematic name.

I doubt that this is the longest systematic name ever used for a synthesised and fully characterised compound. What is?

PS I'm sure we can name many proteins using stupidly long names, but I suspect that is cheating. Let's stick to lab-made compounds and the published literature.