texts: How is a reaction with more products than reactants spontaneous?

texts:
If I have a reaction that has $\Delta G^\circ = 0,$ where there are more products than reactants (for example, $\ce{A <=> 2B + 2C}),$ then if I change the concentration of all the reactants and products (i.e. to 20 mM), then shouldn't the reaction favor the reactants, since you have more total product than reactants (in my example, you would have 40 mM of both $\ce{B}$ and $\ce{C}$ and then just 20 mM of $\ce{A}),$ and therefore produce a positive $\Delta G$ value? I get that if you use the equation $\Delta G = \Delta G^\circ + RT\ln Q,$ you would get a negative $\Delta G$ for my example, showing that it is a spontaneous reaction.

However, can anyone explain this problem from a conceptual perspective, since it would seem that if you have more products than reactants with $Q,$ that would drive the reaction to favor the reactants, according to Le Chatelier's principle?


texts: Raman database of polymer spectra for analyses in R/python

texts:
Can anyone reccomend a raman database of polymer spectra that is open source or freely available? I'm analyzing spectra of a number of plastics and looking for reference spectra for identification.

The majority of available databases are stored in proprietary file formats that don't allow them to be pulled in to conventional scripting analyses in R/python, etc.

Thank you.


texts: Enantioselectivity of Noyori Asymmetric Hydrogenation

texts:
I'm unable to understand the enantioselectivity of Noyori's hydrogenation reaction, and would appreciate any help with the same:

Here's a mechanism I found on Wikipedia:

but, to my disappointment, the highlighted statement, i.e. The (R)-BINAP-Ru catalyze the synthesis the (R)-Product, and the (S)-BINAP Ru catalyze the synthesis the (S)-product with high ee. contradicts the attached paper about Noyori's hydrogenation.

The last two entries of the table mention formation of S products from R-BINAP.

Also, I feel it's not really possible to determine the absolute configuration beforehand, i.e. without knowledge of surrounding groups.

It'd be great if someone could describe the mechanism based enantioselectivity of this reaction in detail, so that correct predictions about the stereochemistry of the product can be made, given the catalyst (R or S BINAP) and the substrate.

Thanks in advance!


texts: 4-Bromophenol vs 4-aminophenol pKa in water comparison confusion

texts:
Recently the other week, I was asked the following question:

  Would you expect 4-aminophenol to have a higher or lower pKa than 4-
  bromophenol when measured in water?

And I thought about this on the way home, and decided to try and justify this using resonance.

My feeling was that Nitrogen couldn't handle 4 bonds and an extra lone pair on its atom, so the negative charge won't leave the benzene ring, whereas the Bromine could handle the double bond (I might have been mistaken with the negative charge on the Bromine - if so, do let me know please.)

Using this, I thought that this is the reason why 4-aminophenol would have a higher pKa than 4-bromophenol as its resonance form is not as extended as Bromine's, which is at a lower energy level to be able to handle the extra negative charge, plus all the carbons in the ring have 4 bonds as normal.

Is this a correct answer and justification?


texts:
When naming compounds, sometimes when there are two vowels in a row the second is elided: this happens for example with "mono-oxide", which becomes "monoxide" instead.
Why is this not always applied, e.g. with "diiodine"? Why aren't the repeated i's removed to make it "diodine"?


texts: What are better acids for removing rust from an iron nail than phosphoric, or oxalic acid?

texts:
I'm planning to conduct an experiment in which I test how fast rusting occurs with changes to the concentration of NaCl in the solution.

I want to measure that by finding the change in mass of an iron nail over time, but in order to do that I need to clean off all the rust on the nail before weighing. I have a relatively short time to conduct the experiments.

I've heard acids like phosphoric acid, oxalic acid, or citric acid will work. I'm looking for the best acid to separate the rust from the nail preferably without using steel wool or any abrasive method. I can, however, spray down the nail with distilled water if necessary. Any suggestions?


texts: Why doesn't frozen sugar solution taste sweet?

texts:
I'll try to make this as brief as possible:

Dissolved two teaspoons of table sugar (sucrose) in about 250ml water. Sipped it, and as expected it tasted sweet. I let the rest of it sit in the freezer overnight. Next day, I took out the frozen sugar solution and, well, licked it.

Surprisingly, I could barely taste any sugar in it. It was almost as though I was licking regular ice.

Why is it that I'm not able to perceive any sweetness here?

I was under the impression that since the solution, being a homogeneous mixture of sugar and water, was sweet, the "popsicle" I made ought to taste sweet too (since the sugar would be evenly distributed over the volume of the ice).


texts: Finding all Chemical Reactions Given Products and Reactants

texts:
Suppose only a set of chemical formulas is given. How can you find all mathematically possible chemical equations whose educts and products are only from this set?

Take e.g. the set $\{ \ce{C, H2, O2, N2, CO, CO2, H2O, NH3, NO, NO2, NO3}\}$.

Or consider e.g. the example in MathStackexchange: Finding all chemical equations (Linear Algebra).

To find all combinations and partial reactions between such given species by hand, is possibly incredibly tedious or near impossible for more complex chemical reaction systems.

I guess these methods are topic of Mathematical Chemistry, Computer Chemistry or Chemoinformatics.


texts: Derivation of Ideal Gas Law with Boltzmann's Constant

texts:
I was reading about the Kinetic Theory of Gases and I came to know about This Particular equation which piqued my interest.

I know about the Ideal Gas Law which gives us $PV=nRT$.
But this one contained Boltzmann's Constant and it goes like this $PV=Nk_BT$ where  $k_B$ is the Boltzmann constant and  T the absolute temperature.
Could I get some insights to how was this form of Ideal Gas Law Derived?
And how was the value of $k_B$ and $R$ determined ? Any help would be appreciated.


texts: Phase of reaction between glucose and potassium cyanide to form amygdalin

texts:
I'm trying to write a detective-fiction novel, and I was wondering if potassium cyanide reacts with sugar only if the glucose for the amygdalin to form is dissolved in liquid or does it react even if the glucose is still sugar, like sugar cubes?
For example if potassium cyanide was mixed in a sugar canister. Will there be amygdalin or will there be amygdalin only if the potassium and sugar from the canister are mixed in a glass of water?
I can't find the answer in google, and I'm not that good with chemistry.


texts: Can Carbon Form bonds without Hybridization?

texts: Carbon has two electrons in its p orbital which should be able to form bonds, are there any examples in which this occurs instead of carbon hybridizing before bonding?


texts: When heat is increased, does water move upward in a straw due to increased capillary action or increased pressure?

texts:
I left a water bottle with an internal straw in my car throughout a long, hot day. When I opened the bottle at the end of the day, water immediately splashed out from the straw. This made me wonder if the increase in temperature caused the liquid to move with greater capillary action upwards in the straw due to higher movement of $\ce{H2O}$ atoms OR whether it was an increase in pressure that led the water molecules to automatically expel outwards from the straw once the bottle was opened.

I know this may seem like a silly question but what explanation would you give for the expulsion of the water from the straw? (I find this recurring event strange because the shape of the bottle never shrinks at all from the heat yet something forces the water outwards but I cannot discern what force causes this. By the way, this never happens to me with regular water bottles - only with ones containing straws/tubes on the inside.)


texts: Quantum and organic chemistry of vitamin D synthesis

texts:
I am somewhat confused by certain steps in this mechanism.

To start with, in the conversion of 7-dehydrocholesterol to previtamin D3, how does the UV photon affect the pi-orbital system in such a way as to rearrange the bonds as shown in the diagram? Else, what exactly brings about the change shown?

Similarly, in the thermal isomerisation step from previtamin D3 to Vitamin D3, what quantum effects and other changes cause the rearrangement shown?

Since this is a biological reaction within the human body it also takes place under physiological conditions ($37^\circ C$, 1 atm, pH = 7.4, various intracellular ionic concentrations).


texts: What is the number of electrons being transferred in electrolysis of aluminum oxide?

texts:
$$\ce{ 2/3 Al2O3 -> 4/3 Al +O2}$$
As we know, to find the Gibbs free energy, we need to use this formula:
$$ G= -nFE^\circ$$
What would $n$ be in this case? After breaking it down into the half reactions $n = 12,$ but this doesn't seem right.


texts: Assign stereodiscriptor to 4th carbon of 3-ethyl-2,4-dimethly-5-(propan-2-yl)heptane-1,7-diol

texts: Here is the molecule. Clearly the 4th carbon is chiral. I have drawn the diagraph for it, but the exploratory pathways of the left and right chains are the same. So, the problem is that the two chains are actually different, but same in the diagraph. How to assign stereodiscriptors in such cases?


texts: Alkali and alkali earth metal carbonates and bicarbonates decomposition

texts:
Which of the following can not decompose on heating to give $\ce{CO_2}$?

$\ce{Li_2CO_3}$
$\ce{Na_2CO_3}$
$\ce{KHCO_3}$
$\ce{BaCO_3}$

What I have read till now: Lithium carbonate is not so stable to heat and bicarbonates of alkali metals decompose at approximately $\pu{300 ^\circ C}$. The stability of alkaline earth metals increases down the group and they decompose on red heating.
This only leaves us with one option as correct (2nd), but what is the reaction of decomposition of $\ce{Na_2CO_3}$?


texts:
In this lecture from MIT, the professor defines the intensity of a wave as the square of the amplitude of the wave. But, at the same time, the professor defines the intensity of light as the number of photons per second. Are these definitions equivalent?

I know that light has both properties of a particle and properties of a wave, but the two different definitions of intensity have different units, which seems confusing to me.

Additionally, when I searched up intensity on Wikipedia, I was unable to find a definition of intensity that matched the definition provided in the lecture. Some of the definitions of intensity that I did find on Wikipedia were "power per unit area," "power per unit solid angle," and "luminous flux per unit solid angle."

Thus, my question is: what do the terms "intensity," "intensity of light," and "intensity of a wave," mean? What are their definitions?


texts: Difference between the terms "autocatalysis" and "(branching) chain reaction"

texts:
Is there a technical difference between the terms "autocatalysis" and "branching chain reaction"? They both seem to refer to something very similar, namely sequences of reactions in which one of the intermediates is also one of the products, leading to the possibility of exponential growth. Is one of the terms more specific than the other, or are they generally understood to mean the same thing?

There do seem to be some differences in how the terms are used. I've never seen the formose cycle, for example, referred to as a chain reaction, which does seem to imply that the term "chain reaction" means something more specific. If this is the case, what is the defining difference between the two terms?

Here is a diagram of the formose cycle (from the German Wikipedia entry, because it has a much better diagram than the English one) - is there a specific reason why it would not be referred to as a chain reaction?


texts:
I study in class 12, and have a doubt in vapour pressure that my school teacher  and my friends are not able to clarify.
My doubt is the reason why the partial vapour pressure of each individual component of a solution is not equal to their respective standard vapour pressures($P°$)?
My reasoning is that consider you have a pure liquid A in a closed container, the vapour pressure of it shall be equal to $P°_A$. Now when you add another volatile liquid B, a solution should be formed; however, the equilibrium of the reaction
$$\ce{A_{liq} <=>  A_{vap}}$$ should not be affected since the concentration of reactants and products remains the same since B is different from A. Eventually, the reaction of B must also reach equilibrium, independently, and thus the partial pressure of B  must be equal to $P°_B$ .
However, this does not seem to be the case. Could someone please help in clarifying my doubt through the viewpoint of equilibrium(Mathematically if possible) and not the standard explanation that the surface of the solvent get's blocked by the particles of the solute, hence the vapour pressure reduces.
Regards,
Arun


texts: Why is heating increasing the solubility of sodium hydroxide?

texts:
\begin{align}
\ce{NaOH &-> Na+ + OH-} & \Delta H^\circ &= \pu{-44.51 kJ/mol}
\end{align}

The dissolution of sodium hydroxide in water is an exothermic process, and so, according to Le Chatelier’s principle, cooling the container should shift the reaction to the right. Shouldn’t this mean that cooling the container will increase the solubility?

According to a solubility chart for sodium hydroxide, heating the container will increase the solubility; why is this the case?


texts: Why is the molecular peak not observed in the mass spectrum of 2,2-dimethylbutane?

texts: Why isn't the molecular weight of 2,2-dimethylbutane on the mass spectrum? I can tell that a $\ce{-CH3}$ group is removed just by the math, but I do not know the reason why. The molecular weight is 86 and I know it has to do with fragmentation.


texts: Number of diastereomer pairs of 1,3-dichloro-1,2,3-triphenylpropane

texts:
How can I determine the number of possible pairs of diastereomers here?
My first guess was two: RR with RS and SS with RS. But what about the potential chirality center middle carbon? There are two identical branches attached to it; however, those two branches can change R/S. So, is it a chirality center?


texts: dipole–dipole interactions: OCR Sample Paper wrong?

texts:
I was doing OCR A Level Chemistry A, H432/01 Periodic table, elements and physical Sample Question Paper.

Question 6 was:

The boiling point of hydrogen bromide is –67 ºC.

The boiling point of hydrogen iodide is –34 ºC.

The different boiling points can be explained in terms of the strength of bonds or interactions.

Which bonds or interactions are responsible for the higher boiling point of hydrogen iodide?

I put answer C: permanent dipole–dipole interactions
?
The given answer was D: induced dipole–dipole interactions

[Revision post down-vote]

My learning to date is that:

dipole-dipole interactions could only be one or the other i.e. permanent or induced.
iodine is more electronegative than hydrogen, therefore the interactions are permanent.

Please would someone explain where how the induced interactions are caused?


texts:
In short

I'm looking for an acid that can solve a polyester, fiberglass composite. However it cannot damage steel.

First of all i like to say that i'm not a chemist. I work in a plastic moulding company. Let me sketch a background.
We make bars out of a polyester strengthened by fiberglas. To make this we have the two materials beeing pulled through a heated steel pipe (the mould). The polyester melts around the fiberglass and forms a strong lightweight pole. However sometimes the pole breaks mid process and then there is a part that's stuck in the mould. Like in the picture

It's very hard to remove the polyester/fiberglass bar from the mould, dare I say near impossible.

I was wondering if there is an acid that solves the polyester but makes no damage at all to the chrome steel mould.


texts:
When chloral undergoes reaction with a concentrated alkali, will it undergo Cannizarro reaction to form the corresponding alcohol and acidic salt, or should it form chloroform instead by departure of trichloro carbanion instead of the hydride ion?

I understand that the trichlorocarbanion is stabilized by the $-I$ effect of chlorine, so why not form that instead?


texts: Should the 'a' in the acid dissociation constant (Ka or pKa) be capitalised?

texts:
In science, the negative logarithm of the acid dissociation constant is denoted $\mathrm{p}K_\mathrm{a}$ or $\mathrm{p}K_\mathrm{A}$ depending on the source (lowercase "a" or uppercase "A"). Since it is related to the acid dissociation constant, defined as

$$K_\mathrm{A} = \frac{[\ce{A-}][\ce{H3O+}]}{[\ce{AH}]}$$

I would write $\mathrm{p}K_\mathrm{A}$ (the LaTeX package chemmacros renders it so, but doesn't give any source it in its documentation). It seems to me that $\mathrm{p}K_\mathrm{a}$ is the "modern" version of pKa, which was written like this in the last century because of the lack of subscript character on typesetting machines.

I cannot find any source or styling guide saying explicitly which one should be used today (like the IUPAC Green Book), and why.


texts: Determining the acid dissociation constant change with temperature in sparkling water

texts: I already have the different values of pH at the different temperatures, but what I'm trying to figure out is obtaining the acid dissociation constant using these pH values. Is there a way I can do that without having the initial and final concentrations of CO2 in the sparkling water or would I have to do an extra step?


texts: Why does LiAlH4 reduce the double bond of cinnamaldehyde, whereas NaBH4 does not?

texts:
I read an answer here about why $\ce{LiAlH_4}$ does not reduce conjugated double bonds, and that $\ce{NaBH_4}$ does. But in the case of cinnamaldehyde, $\ce{LiAlH_4}$ reduces the conjugated double bond and $\ce{NaBH_4}$ does not. Why is it so?

Citation for $\ce{LiAlH_4}$: Quora

Citation for $\ce{NaBH_4}$:

Image Source


texts: How to synthesize Boron tri-fluoride using Boron Oxide

texts:
I am finding different equations for the synthesis. My lecture handout suggests a reaction with Sodium tetrafluroborate and Sulfuric acid. This is fine but I have to remember this for an exam and that reaction looks extremely hard to remember/balance in an exam. A second way seems to be reaction of boron oxide with Calcium fluoride and Sulfuric acid. However, I cannot find consistent equations for this...

Wikipedia simply suggests that Boron oxide reacts with $\ce{HF}$ which is made in situ by the reaction between sulfuric acid and calcium fluoride:

$$\ce{B2O3 + 6HF -> 2BF3 + 3H2O}$$

It's easy to remember but I am reluctant to accept this because it excludes two of the reactants (sulfuric acid and calcium fluoride). Would it be acceptable to merge the formation of $\ce{HF}$ into the above equation - thus including all reactants:

$$\ce{B2O3 + 3CaF2 + 6H2SO4 -> 2BF3 + 3H2O + 3Ca(HSO4)2}$$

It's a little tricky to balance but not too hard to remember. Is there anything wrong with the above equation? I haven't seen it anywhere but only variations on it.


texts: How does the equilibrium shift when the products are solid and gas when increasing pressure?

texts:
$$\ce{CaCO3(s) <=> CaO(s) + CO2(g)}$$
How will the amount of each element change if the pressure is increased?
My guess is that the equilibrium will shift to the left, because the right side has 1 gas molecule. I know my solution contradicts with Le Chatelier's principles, but there is no gas on the left. So how will the the amount of the elements on the right decrease and the solid on the left increase since pressure only has an effect on gases.


texts: Calculating the pH of a weak acid from the Kb of its conjugate base

texts:
I'd start off by saying it's been many years since I was in chemistry lessons and have forgotten much, but recently I have had to relearn a lot of basic chemistry. The following doesn't really impede me in my work, but it irritates me that I can't figure out what is basically two sides of the same coin.

Let's imagine I want to calculate the pH of a 0.1M acetic acid ($c_\ce{CH3COOH} = \pu{0.1M}$)

Acetic acid is a weak acid and dissociates in water as follows: $\ce{CH_3COOH + H_2O <<=> CH_3COO^- + H_3O^+}$. Expressing this in terms of acid dissociation constant (and ignoring the water) yields $K_\mathrm{a} = {\large{\ce{\frac{[CH_3COO^-][H^+]}{[CH_3COOH]}}}}$

We can look up the $K_\mathrm{a}$ of acetic acid, which is $1.8 \times 10^{-5}$. If we assume that the amount of $\ce{CH_3COOH}$ change is negligible (due to it being a weak acid and only slightly dissociating), and that $\ce{CH_3COO^-}$ and $\ce{H^+}$ concentrations are equal, we come up with the following equation:

$1.8 \times 10^{-5} = \large{\frac{[\ce{H^+}]^2}{\pu{0.1M}}}$

Rearranging and solving for $\ce{[H^+]}$ gives us $\sqrt{1.8 \times 10^{-5} \times \pu{0.1M}} = \pu{1.34E-3 M}$

Since $\mathrm{pH} = -\log([\ce{H+}])$ (or $\mathrm{pH} = \log(1/[\ce{H+}])$, whichever you prefer), $\mathrm{pH} = -\log(1.34 \times 10^{-3}) \approx 2.88$

I've checked this and I know it's correct. But I don't know how to do it from the $K_\mathrm{b}$. Or rather, I get the answer, but I don't fully understand the process.

So the opposite reaction, $\ce{CH_3COO^- + H_2O <=>> CH_3COOH + OH^-}$, also has a equilibrium constant which is called $K_\mathrm{b}$, defined as follows (again ignoring the water):

${\normalsize K_\mathrm{b}} = {\large \ce{\frac{[CH_3COOH][OH^-]}{[CH_3COO^-]}}}$

We can look it up or calculate it from the relationship that $K_\mathrm{a} \times K_\mathrm{b} = 1\times10^{-14}$

$K_\mathrm{b} = {\large \frac{1\times10^{-14}}{K_\mathrm{a}}}$

In either case, $K_\mathrm{b} = 5.6 \times 10^{-10}$

Now, I don't know what to do with the $\ce{[OH^-]}$. My basic assumption is that the change in the amount of $\ce{CH_3COOH}$ is negligible, so that stay as 0.1M. But unlike previously where $\ce{CH_3COO^-}$ and $\ce{[H^+]}$ were formed in equal amounts due to the dissociation of the acid, how much of $\ce{[OH^-]}$ is there? My (wrong) logic was to assume that $\ce{[CH_3COO^-] = -[OH^-]}$, but then they cancel out, leaving me with $K_\mathrm{b} = \ce{[CH3COOH]}$, which can't be right. So yeah, I'm lost.

I solved this by substituting $\ce{[OH^-]}$ with $\large{\frac{K_\mathrm{w}}{[\ce{H+}]}}$ (because $\ce{[H^+][OH^-]} = K_\mathrm{w}$)

This yields ${\normalsize K_\mathrm{b}} = {\large \ce{\frac{[CH_3COOH] K_w}{[CH_3COO^-][H^+]}}}$. Again assuming that $\ce{[CH_3COO-]} = \ce{[H+]}$, and knowing that $K_w = 1 \times 10^{-14}$, I come up with ${5.6 \times 10^{-10}} = {\large \ce{\frac{0.1M \times 1 \times 10^{-14}}{[H^+]^2}}}$

Solving for $\ce{[H^+]}$ gives us $\sqrt{{\large \frac{\pu{0.1M} \times 1 \times 10^{-14}}{5.6 \times 10^{-10}}}} = \pu{1.33 \times 10^{-3}M}$

This is the same concentration of $\ce{[H^+]}$ that I got using the $K_\mathrm{a}$ above, making the $\mathrm{pH} = -\log(1.33 \times 10^{-3}) \approx 2.88$

So I can get to the same answer ignoring (or rather substituting) the $\ce{[OH^-]}$, but I'd really like to know how to do it using that. This is probably a really simple answer but after having spent many hours staring my many pieces of paper, my mind is coming up with a blank.


texts: Does the rate of dissociation of PCl5 increase in presence of Cl2

texts:
I'm sorry if this is somehow inappropriate to ask but I've found a rather strange question on my text book that asks "Why does the rate of dissociation of $\ce{PCl5}$ increase in the presence of $\ce{Cl2}$ ?".

Somehow I couldn't find any relevant answer to this question, which led me to possibly believe that this might be a printing mistake. But nonetheless I wanted to ask if this particular case is an exception or not.


texts: Why is the boiling point of CH3COOH higher than that of C2H5OH?

texts: Why is the boiling point of $\ce{CH3COOH}$ higher than that of $\ce{C2H5OH}$ ? Both are polar molecules held by hydrogen bond.


texts: According to IUPAC rules, am I right in assuming that butanone is sufficient, because there's only one possible molecule? I keep noticing butan-2-one, so I want to make sure.


texts: In Crystal Field Theory what does Δo=10Dq mean?

texts: While studying the Crystal Field Theory I was told $\mathrm{Dq}$ is a unit, related to the unit $\Delta_{\mathrm{O}}$ by the relation $\Delta_{\mathrm{O}} = 10\ \mathrm{Dq}$. But aren't $\Delta_{\mathrm{O}}$ and $\mathrm{Dq}$ variables, not units? The unit is of energy, such as $\mathrm{eV}$ or Joules, these are symbols to represent a particular value of energy, which could be anything. So what do we mean when we say $\Delta_{\mathrm{O}}= 10\ \mathrm{Dq}$? What exactly is $\mathrm{Dq}$ (I haven't been able to find this in any of my textbooks, they just either state this relation, or not at all) and are they actually units of energy?


texts:
Why and how are azeotropes formed?

I could not find a detailed explanation of how azeotropic mixtures are formed anywhere on the internet. Now, that I figured it out myself, I thought I'd share it.


texts: Nomenclature of methyl groups in an alkanol

texts:
I'm having trouble with this question since I'm getting (A), when the answer says its (B).

My logic was that there is a methyl group on the first carbon, and a hydroxide functional group on the second carbon, hence the name 1-methyl-2-pentanol.

Could someone please explain why I am wrong?


texts: About dative covalent bonding and expanded octet rule

texts:
I'm beginning my studies of chemistry at high school (I'm not a native English speaker, though) and I have some basic questions:

1)  Consider the compound xenon tetroxide. In this molecule, does the xenon have its valence layer expanded? In another words, the oxygen atoms only have double covalent bonds with the Xenon?

I've tried to look for this answer but I'm still in doubt whether xenon does four dative covalent bonds (with each oxygen) or four double covalent bonds. In the first case, does not occur the expanded octet rule for xenon, right?

2) Another question; is it possible for a dative covalent bond to occur with just one electron? I mean, the atom which has more electrons in its valence layer "donates" just one electron instead of two? If the answer is "yes", can you provide me an example, please?

I'm sorry for the English mistakes. I started to learn this "chemistry vocabulary" just now.


texts:
Why is it that
$$\mathrm{p}K_\mathrm{a}(\ce{HF}) < \mathrm{p}K_\mathrm{a}(\ce{HCl}) < \mathrm{p}K_\mathrm{a}(\ce{HBr}) < \mathrm{p}K_\mathrm{a}(\ce{HI}),$$
even though the electronegativity decreases down the group? The more electronegative the atom accompanying hydrogen, the lower the energy of the σ* bond. The lower the energy of the σ* bond, the easier it is for nucleophiles to attach to it (i.e. hydrogen is more easily removed from the compound, thus making it more acidic).
Obviously, something is wrong with this reasoning. I could guess it is because hydrogen binds to different $\mathrm s$ orbitals with the different halogens. For $\ce{F},$ $\ce{Cl},$ $\ce{Br},$ $\ce{I}$ these are $\mathrm{2sp^3},$ $\mathrm{3sp^3},$ $\mathrm{4sp^3},$ $\mathrm{5sp^3},$ respectively.


texts: Why is the groundstate electronic degeneracy of monoatomic O(g) 5?

texts:
A problem in my Pchem textbook states that the electronic degeneracy of an oxygen atom is 5. My reasoning leads me to believe that the degeneracy is actually 6 (S = 1, L = 1, so (S+1)(L+1) = 6. This would indicate there are two unpaired electrons and a pair in the P orbitals...

The only way I can reason a 5 degeneracy is if the ground state has a pair in the d-orbitals, which I do not believe is the case.


texts: Is there a physical explanation why benzene's pi molecular orbitals in a Frost circle are degenerate but pyridine's are not?

texts:
From here, the Frost Circles for both benzene and pyridine:

The $\pi$-MOs formed by 6 $\pi$-AOs of an aromatic ring are:

Listed with respect to the ordering in the above image, these MOs in benzene's $D_{6h}$ symmetry correspond to the group representations:

$\pi_6=B_{2g}$

$\pi_4 / \pi_5=E_{2u}$

$\pi_2 / \pi_3=E_{1g}$

$\pi_1=A_{2u}$

The $D_{6h}$ symmetry of benzene is reduced to $C_{2v}$ in pyridine. I believe the pyridine MOs transform in $C_{2v}$ symmetry as:

$\pi_6=B_2$

$\pi_5=B_2$

$\pi_4=A_2$

$\pi_3=A_2$

$\pi_2=B_2$

$\pi_1=B_2$

Onto my question:

Because the doubly degenerate $E$ representation does not exist in the $C_{2v}$ symmetry of pyridine, the corresponding $\pi$ orbitals are no longer degenerate. I could just stop there and accept that symmetry dictates degeneracy and there's nothing more for me to understand, but is there a way to dig a level deeper and connect the degeneracy to a physical explanation?

For example, I can imagine nodes breaking the extended conjugation of the $\pi$-atomic orbitals, which would explain why the $\pi$-MO with zero nodes is the lowest energy bonding orbital, and the $\pi$-MO with the most nodes the highest energy antibonding orbital. In this way, I can understand why the pyridine MOs climb in energy with increasing nodes. However, if it were solely about nodes and conjugation, then the benzene $\pi_2 / \pi_3$ and $\pi_4 / \pi_5$ MOs should not be degenerate; the one with more nodes would be higher lying in energy.

Or maybe the $\pi_3$ MO in pyridine is higher in energy because it has no $\pi$-atomic orbital situated on the nitrogen atom—the node is located on the nitrogen. Nitrogen being more electronegative than carbon, there should be a lower potential with some electron density localized in an atomic orbital on nitrogen. Therefore, the $\pi_2$ MO would lie lower in energy than its $\pi_3$ counterpart because nitrogen possesses an atomic orbital in the $\pi_2$ MO.

Is there a physical explanation why these orbitals in benzene are degenerate, and vice versa why the corresponding orbitals in pyridine are not?


texts: Counting valency of atoms, in a molecule with python

texts:
The documentation for the indigo module can be found here

http://ggasoftware.com/opensource/indigo/api#inputoutput

So for instance if I have a molecule object for some SMILES string, e.g. "[C](=[O])", I wish to calculate the valency of each atom, for instance here the desired output would be [atom=C, unbound_electrons=2],[atom=O, valency=0]

If I consider the atom "[C]"
Can anyone explain why is this code printing [atom=C, unbound_electrons=0] not [atom=C, unbound_electrons=4]

from indigo import *
indigo = Indigo()

mol=indigo.loadMolecule("[C]")

print(mol.grossFormula(),"\n")

for atom in mol.iterateAtoms():
        print([atom.symbol(),atom.radicalElectrons()])

EDIT: I could work it out if I could generate a list of the types of bonds on the atom in conjuction with atom.atomicNumber(). E.g. if I could say [C] has a double bond I could take it's atomic number - 2 (second shell) - 2 (double bond)

EDIT#2: This might be useful for visualising what i'm talking about

from indigo_renderer import *
renderer = IndigoRenderer(indigo)
renderer.renderToFile(mol,"mol.png")

EDIT#3: I am not a chemist, so might have got some concepts wrong


texts: Clausius–Clapeyron relation for states of water and vapor

texts:
I've seen many questions about this topic on this site, but I still have some issues trying to understand this aspect. Here's what I believe I understood
looking at the phase diagram for a pure substance (water):

If you put water in a container with a piston pushing $\pu{1 atm}$ directly on the water with no extra space for inert gases, it will stay 100% liquid as at room temperature and $\pu{1 atm}$ liquid is the stable phase.
If the water is put at room temperature in a closed box where the volume is more than the volume of the water (creating a vacuum), the molecules will evaporate in a number so that the water vapor will be at the equilibrium pressure corresponding to room temperature, which can be calculated by the phase diagram.

I can't understand why the air (and its pressure) doesn't work like a piston, making sure no water is in gas state at $\pu{1 atm}$.

In particular, there was this exercise where a piston with $p = p_\mathrm{tot}$ was pushing down on a mixture of vapor $\ce{A}$ and inert gas above pure liquid $\ce{Ar}$, so that:

\begin{align}
p_\mathrm{tot} &= p_\mathrm{inert} + p_\mathrm{a}\\
\text{Equilibrium:}\qquad \ce{A(l, $p_\mathrm{tot}$) &= Inert(g, $p_\mathrm{inert}$) + Vapor(g, $p_\mathrm{a}$)}
\end{align}

Why doesn't the vapor $\ce{A}$ 'feel' the $p_\mathrm{tot}$ and get condensed into liquid $\ce{A}$?

Was it because $p_\mathrm{tot}$ is less than the vapour pressure of pure $\ce{A}$ at that temperature? If it was $p_\mathrm{tot} = p_\mathrm{vap}$ ($T = T_\mathrm{exercise}$), then the equilibium would be

$$\ce{A(pure, l, $p_\mathrm{tot}, T$) = Inert(g, $T, p_\mathrm{tot}$)?}$$

This doesn't look like an everyday case to me though where water is in gas form even if the pressure is $\pu{1 atm}$.


texts:
I am a journal typesetter, and recently I came to a problem that I'm not sure I know to solve. The question is how to properly typeset the "NOx" abbreviation for nitrogen oxides. Which is typographically correct:

$\mathrm{NO}_x$ (because $x$ is a numeric variable); or
$\mathrm{NO}_{\mathrm{x}}$ (because all names of chemical compounds are strictly upright)?


texts: Denaturing of Proteins and Nucleic Acids - Effect of Temperature (Heating vs Cooling)

texts:
Heating a protein/nucleic acid will disrupt inter-molecular and intra-molecular forces in the tertiary structure. It will also interfere with the shape of the active site if the protein.

Does this apply with cooling also?


texts: Ammonia and hydroxide ion - Lewis basicity

texts:
Which is the stronger Lewis base, and why?

I'm thinking that the answer is "it depends." With regard to the hydrogen proton, which hydroxide ion is obviously the stronger Lewis base. However, with regard to other, more complex Lewis bases, the distinction may not be so clear, as hydroxide ion has several lone pairs (three) and these can weaken the stability of Lewis adducts through lone pair/"bonding pair" (the pair that forms the coordinate covalent bond) repulsions. Ammonia only has one lone pair so there isn't an issue of lone pair/"bonding pair" repulsion.


texts: Rationalising the order of reactivity of carbonyl compounds towards nucleophiles

texts:
This is immediately following ron's answer from Why is a ketone more nucleophilic than an ester?

One of the most simplest questions you can ask, how can you rationalise the order of reactivity towards nucleophiles, which is given as

acyl halide > acid anhydride > aldehyde > ketone > ester ~ carboxylic acid > amide > carboxylate ion

There might be many concepts out there, that explain this order, the above linked question could only halfway satisfactory answer it in the kind of generality I am looking for.

I am looking here for any model that can be used to explain this reactivity.

I will also later on post an answer to this question using quantum chemical calculations, trying to generalise from example. The key points that will be included are stated in ron's answer linked above.

  I like Martin's posts, they make me think - and that is always a good
  thing. Here is where my thinking has taken me:

  I believe Martin's approach (basically frontier MO) is fundamentally
  correct. I would be more convinced that his actual numbers are
  meaningful if he were to calculate 1) the carbonyl carbon LUMO
  coefficient and 2) the HOMO-LUMO separation for the following series
  of compounds in order to see if his calculated values correlated with
  this order of reactivity of carbonyl compounds towards nucleophilic
  attack (we could use water as the nucleophile) - but Martin, I think
  such calculations might be a poor use of your time and resources.

While I agree with most of this, I do strongly disagree with the last statement. Which I will hopefully be able to prove soon.

In the meantime I welcome everyone to share their thoughts on the matter.


texts: Why can dissolution reactions (e.g. dissolution of calcium chloride) be exothermic?

texts: Dissolution reactions are normally endothermic, and crystallization reactions are normally exothermic, but there are some exceptions -- such as the dissolution of calcium chloride. Why is this so?


texts: Can we synthesize alcohols by the photolysis of hydrogen peroxide?

texts:
As I was going through my revision of organic chemistry, I came across free radical substitution of alkanes with halogens. In a similar process where we use hydrogen peroxide, instead of chlorine, so that photolysis would yield a hydroxide radical $\ce{OH.}$ instead of chlorine radical $\ce{Cl.}$. The rest of the steps would be the regular mechanism of This way we can get an alcohol instead of alkyl chloride. Here is what I mean:
\begin{align}
  \ce{H-O-O-H &->[h\nu]H-O. + .O-H}\\
  \ce{CH3-CH3 + .O-H &-> CH3-CH2. + H2O}\\
  \ce{CH3-CH. + .O-H &-> CH3-CH2-OH}\\
\end{align}

Does my hypothesis work in reality?

I am aware of the fact that dialkyl peroxides cannot be used since they are highly explosive. However, hydrogen peroxide isn't that explosive, so I think that its safe to use it. Since $\ce{H2O2}$ is a liquid, while alkanes and $\ce{Cl2}$ are gases, the reaction with $\ce{H2O2}$ could be done at low pressure. We could photolyse the $\ce{HO-OH}$ bond using light of a sufficient frequency, which probably should initiate a free radical reaction.

I did a few calculations and got the maximum wavelength of light needed to photolyse the $\ce{O-O}$ bond is $\pu{0.0084m}$, which is pretty low. So I think it's possible to photolyse $\ce{H2O2}$ and carry on the reaction.


texts: What is the amount of nitrate ions in 20 g of Fe(NO3)3?

texts:
What is the amount of nitrate ions in $20.0\:\mathrm{g}$ of $\ce{Fe(NO3)3}$?

The chemical formula for the nitrate ion is $\ce{NO3}$, I think.

The molar mass of $\ce{Fe(NO3)3}$ is $242~\mathrm{g~mol^{-1}}$ of which $186\ \mathrm{g\ mol^{-1}}$ belong to $\ce{NO3}$. That means that around $76.85\:\%$ of the substance is nitrate ion.

$20.0\ \mathrm g$ of the substance are equivalent to $20.0\ \mathrm g/242\ \mathrm{g\ mol^{-1}} = 0.0826~\mathrm{mol}$ of $\ce{Fe(NO3)3}$.

Since roughly $76.85\:\%$ are nitrate ions, there are about $0.06~\mathrm{mol}$ of nitrate ions in those $20\ \mathrm g$ of substance.

One mole is $6.02\times 10^{23}$, so if I multiply $(0.06\ \mathrm{mol})(6.02\times 10^{23}\ \mathrm{mol^{-1}}) = 3.612\times10^{22}$.

My Answer: There are $3.612\times10^{22}$ nitrate ions in $20.0\:\mathrm{g}$ of $\ce{Fe(NO3)3}$.

However, that is wrong. The options in the website are:

$1.49\times 10^{23}$
$4.98\times 10^{21}$
$60.0$
$8.25\times10^{21}$

And my answer is not even close to any of them.

What did I do wrong?


texts: Calculating the concentration of a diluted solution

texts:
I have this problem:

From a stock solution of initial concentration of $10~\mathrm{mg/l}$, I take $2\,\mathrm{ml}$, and then I add $10\,\mathrm{ml}$ of distilled water.

I am supposed to calculate the final concentration. I have solved the problem in this way.
$$\begin{align}
C_1 \cdot V_1 &= C_2 \cdot V_2 \\
C_1 &= 10~\mathrm{mg/l} \\
V_1 &= 2~\mathrm{ml} \\
V_2 &= (2~\mathrm{ml} + 10~\mathrm{ml})= 12~\mathrm{ml} \\
C_2 &= \frac{C_1 \cdot V_1}{V_2}  \\
&= \frac{(10~\mathrm{mg/l}) \cdot (2~\mathrm{ml})}{12~\mathrm{ml}} \\
&= 1.67~\mathrm{mg/l}
\end{align}$$
Is this correct?


texts:
In his 1926 thesis Robert Cady Burts describes the production of sodium by electrolysis of sodium nitrate through glass.

I can't find much else on this method. Are there any modern descriptions of the experiment? Videos maybe?


texts: Exceptions to the Madelung rule for electronic configurations

texts:
The electronic configuration of platinum is

$$\mathrm{[Xe] 4f^{14} 5d^9 6s^1}$$

and not $\mathrm{[Xe] 4f^{14} 5d^{10} 6s^0}$ or $\mathrm{[Xe] 4f^{14} 5d^8 6s^2}$.

I see this question has already been answered, but here is what Wikipedia says:

  Other exceptions to Madelung's rule:
  For example, in the transition metals, the 4s orbital is of a higher energy than the $\ce{3d}$ orbitals; and in the lanthanides, the $\ce{6s}$ is higher than the $\ce{4f}$ and $\ce{5d}$.

I don't understand the reason behind this.

Shouldn't it be that the $\ce{4s}$ orbital is of a lower energy than the $\ce{3d}$ orbitals (that's why it is filled first) and in the lanthanides, the $\ce{6s}$ is lower than the $\ce{4f}$ and $\ce{5d}$?

It also states that in heavier elements the inner electrons move with a speed approaching the speed of light. So why don't we consider the great amount of kinetic energy associated with the electron? If we consider this energy then the inner orbitals should not be filled first owing to their great amount of energy?

There is a list of exceptions arising from electronic configurations of lanthanides and transition series.

The exceptions in the transition series are explained by the fact that half and fully filled orbitals are more stable (although my text doesn't state why they are stable)?

So similarly do we have a rule that governs the electronic configuration of lanthanides? I believe for someone who is in his first year Hartree-Fock calculations are not a good thing to start with. So do I need to just memorize them all?


texts: Rearrangements; Carbocations; E1 Mechanism

texts:
If the leaving of the leaving group creates a secondary carbocation, and a tertiary carbocation has the possibility of being formed through a 1,2 methyl shift:

1) Will the methyl shift? I'm guessing the answer is an emphatic yes. Tertiary carbocations are more stable than secondary carbocations.

2) Will there still be some secondary carbocation left over? I.e. will there be both major and minor products? I'm guessing yes.

I ask because I was watching a video on E1 elimination and the narrator ignored the possibility of a shift, and I was wondering if this was because he forgot or because it was irrelevant.


texts: Conductive liquid, that after evaporation will allow me to use my gloves with a smartphone

texts:
I'm looking for a conductive liquid that, after it evaporates, leaves the material that has been exposed to it conductive.

I'd like to use my smartphone with gloves. I do have a pair of professional, expensive gloves, with "smartphone friendly material" on the index finger-pad, but it works dreadfully. I'd like to use the tip of my finger, and not the finger-pad, to interact with the smartphone surface.

So I thought, let's wet the material in some conductive liquid, let it dry, and done!

I did try this approach with colloidal silver and it does not seem to work.

The next on my list is a solution of water with iron rust ( I am unsure about the effect, but I'd give it a try).

Any other ideas? It must be human-safe. Colloidal silver would be perfect (antibacterial properties) if it could be made to work.


texts: Why do the two methylene protons in ethylbenzene have a chemical shift at 2-2.9?

texts: The data sheet does not have any chemical shifts in this range for compounds containing only carbon and hydrogen


texts: Mechanism of the Synthesis of Cyclooctatetraene from Pseudopelletierine

texts:
We've been looking at total synthesis in class and the uses of the products. An example was Willstätter's use of pseudopelletierine to synthesise cyclooctatetraene.

I've just been wondering how the mechanism would proceed and if someone could show me the entire reaction scheme then that would be great.

I think the first step to the mechanism involves a sodium radical attacking the ketone. I'm just a bit intrigued how it would all work.


texts: What determines humidity limit / dew point of the air? - Why can air only hold a certain amount of water?

texts:
From Wikipedia:

  The dew point is the temperature at which the water vapor in a sample of air at constant barometric pressure condenses into liquid water at the same rate at which it evaporates. At temperatures below the dew point, water will leave the air.

I am wondering what is is about the air which determines how much $\ce{H2O}$ vapour can be stored in a set volume of air at a set temperature without the water condensing back to liquid water.
Also, why is it that at higher temperatures the air can hold a greater amount of water vapour?


texts: What is difference between aluminium mercury alloy and gallium aluminium alloy?

texts:
Aluminum mercury alloy is used as a chemical reagent to reduce compounds, such as the reduction of imines to amines,in this case mercury destroy aluminium oxide layer which protect aluminium to react with water.

Alloy of aluminium and gallium which similar to above alloy make the aluminium more reactive by preventing it from forming an oxide layer.

In both cases mercury and gallium plays a same role of destroying oxide layer on aluminium to react with water but why can't gallium aluminium alloy reduce imines to amines like mercury aluminium alloy ?


texts: Does CO2 dissolution in different salt concentrations affects the amount of carbonic acid formed?

texts:
We have a school experiment, where I must report on the following question:

  Does salinity affect the solubility of $\ce{CO2}$ in saltwater?

So we selected four different concentrations of salt (in the range of 1-4 %) in 100 mL of water and added 5 g of $\ce{CO2}$ and measured the time it took to dissolve completely. We then used titration to figure out the amount of $\ce{CO2}$ (reacting with water to give weak carbonic acid) that is dissolved.

My questions are:

Will the amount of $\ce{CO2}$ that reacts with water depend upon the salt concentration?
Will the amount of titrant used to figure out the amount of $\ce{CO2}$ dissolved also change depending on the salt concentrations?


texts:
I'm looking for products that can be used as non-toxic PVC plasticizers.
I've used ATBC as a product that I can add to, for example, the inside of a pool toy, which with time absorbs it and becomes softer.
The problem I want to solve is to find readily available products that are made of ATBC or other non-toxic plasticizer, and that can be absorbed in the same manner.
The only one I've found and used is Sculpey Clay Softener which is composed by 100% ATBC, but this is very expensive:
https://www.amazon.com/-/pt/dp/B0047V7A56/ref=sr_1_13?__mk_pt_BR=ÅMÅŽÕÑ&dchild=1&keywords=sculpey+clay+softener&qid=1608119391&sr=8-13
Are there any other, more common and readily available, items that are composed by ATBC or other product that performs the same task?
An alternative plasticizer that is of higher quality, i.e. leaks out at a smaller rate or doesn't compromise the strength of the material, would be even better. My main objective is to make the item softer, but without making it a lot more susceptible to popping and avoiding products that might be toxic when absorbed by skin.
P.S. Sorry for any lack in formality as my knowledge of chemistry is what I can remember from high school.


texts:
I made a solution of iron acetate by placing steel wool in one litre of acetic acid (vinegar $5\%$) and adding a few tablespoons of hydrogen peroxide of questionable age. The solution turned a nice brown almost instantly upon shaking.

I left it overnight and it lost its colour while forming a white precipitate:

I added some more peroxide (new, good peroxide this time), and the moment the peroxide hit the clear an colorless solution it looked like dark red-brown food-coloring! Unfortunately I could only get out my camera fast enough to make the following photo:

I squeezed the air out of the steel wool before the above picture, which caused it to sink (noted this so you don't think something of its sinking). Added one-fourth cup hydrogen peroxide and shook:

With a flash from the top:

Held up to the light:

The result seems to be ferric acetate (III), since ferric acetate (II) is light brown in color (according to the Wikipedia link)--possibly like the light brown in the first/top photo. Ferric acetate (III) is supposed to be a red-brown color (again according to the Wikipedia link).

It is the clear an colourless solution in the second picture that I am not certain as to its composition. Any assistance will be appreciated in identifying that solution.

I would hypothesize that the white precipitate is either acetate or carbonate (more likely carbonate). I would guess that the clear solution occurred as a result of the solution interacting with either the steel wool or the air. I took the steel wool out after making the final dark red solution and it has been 2 days now without it diminishing in colour, so it is likely not the air that was interacting with the solution. Perhaps, if I placed the steel wool back in the solution, it might go clear again. I'll post again in a day or two.


texts: How to determine bond order for special cases?

texts:
In AP Chemistry, we learned two ways to determine bond order. The first method is: Bond order = (bonding electrons - antibonding electrons)/2. The second method is: number of bonds / number of bond locations.

Applying the first method for the bond order of CO gives an answer of (8-2)/2 = 3. Using the second method, CO has one triple bond which gives an answer of 3/1 = 3.

Both methods also yield the same answer for CO^2+. One important characteristic of this bond is that carbon and oxygen make a double bond instead of a triple bond because the CO molecule is electron deficient. Since there is one double bond and one bonding location, the answer is 2/1=2. The result is the same for the other method as well.

In CO^+, the methods give different results. The first method gives an answer of (7-2)/2 = 2.5. I am unsure of the exact structure of the CO^+. Using a triple bond and leaving either the oxygen electron deficient by one or the carbon electron deficient by one gives an answer of 3. I am not sure how else the molecule can be depicted, perhaps with a delocalized bond somehow? I do not know much about delocalized bonds, so I do not know their rules and limitations. Am I incorrectly drawing the structure and is there a way to draw it so that it can satisfy the second method? Feel free to make edits on my formatting, I am new to this.


texts: A nucleophile should get better at its job if it can donate a pair of electrons more easily. We say that a more electronegative atom should be less nucleophilic , generally. I understand this is because the more EN an atom gets, the more strongly it pulls electrons towards itself. But why does the fact that such an atom would ,generally, have more electron density not override this?


texts: Order of reactivity of nucleophilic addition at carbonyl group with Grignard reagent

texts:
I thought the order would be $1 > 3 > 2$ as 1 is aldehyde and 2, 3 are ketones. As generally aldehydes are more reactive, I placed it first. I chose 3 over 2 as two alkyl groups would make cleaving of $\ce{C=O}$ difficult in 2.

But the answer is given $1 > 2 > 3$, even though phenyl is a bulky group and alkyl groups are electron releasing.

How to approach these type of questions?


texts: Why are the rare earths erbium (Er), terbium (Tb), yttrium (Y) and ytterbium (Yb) named like that?

texts:
I know the history of the discovery of the rare earth elements, that they were discovered near the village Ytterby in Sweden in the 19th century. Four elements are directly named after that village: erbium (Er), terbium (Tb), yttrium (Y) and ytterbium (Yb).

Why are they named like this? It makes sense to name one element after the locality, but why name the rest as misspellings of that village? It's not like we have ermanium, germium and ermium in addition to germanium (although we do have holmium).

This site mentions this:

  In 1842, Swedish chemist Carl Gustaf Mosander separated the "yttria" component found in the mineral gadolinite into three segments that he called yttria, erbia and terbia.

Is the any record as to why Mosander chose these names? Because...

  As might be expected considering the similarities between their names and properties, scientists soon confused erbia and terbia.


texts: Can a six member ring expand to achieve octet completion to stabilize a carbocation?

texts:
(Probably unnecessary background: I came up with this carbocation while predicting the major product of $\ce{NaNO2/HCl}$ with 1-(methylamine)cyclohexan-1-ol)

Will the following carbocation rearrangement occur?

I have opinions both for and against it.

For: The ring expansion leads to octet completion of the empty p orbital of the carbocation. That stabilizes the carbocation.

Against: expansion from six member ring to seven member ring is uncommon. In school, I was taught that - for rings less than size ten - the cyclohexane ring is the most stable ("strain-free"). So, rearrangement shouldn't occur.

A Scholar search gives me no results for the proposed expansion. I know the search probably won't get me anywhere because I don't know the right keywords, and hence I'm stuck. So, can a six member ring expand to achieve octet completion to stabilize a carbocation? Also, does the expansion lead to the major product?


texts:
I came across a question asking me the reason for the lustrous appearance of many metals. The answer stated that it was due to the presence of free electrons in the metal. But I don't understand how this works. How do the free electrons affect the reflection of light from the metallic surface?

Thanks.


texts: Why carbon monoxide reacts with hydrogen to give different products in the presence of different catalysts

texts: My books says how carbon monoxide will react with hydrogen to give different products with different catalysts, but how exactly do different catalysts yield different products. Do they provide different pathways for entirely different mechanisms, or is the formation of some products is better thermodynamically and for that reaction to occur some catalysts provide the necessary activation energy and the others cant.


texts: IUPAC nomenclature of alicyclic compound with an equal number of cyclic and acyclic carbons

texts: In this compound there are three cyclic and three acyclic carbons. Even the substituent comes on the 2nd position in both cases. So, should the main chain be the cyclic one, since there is a rule that cyclic has a priority over acyclic?


texts:
Series A and B below can be viewed in two different ways to annulate an ethano-bridge onto four-, five-, and six-membered rings. Using the $\Delta_\mathrm{f}H^\circ$ values given (in kcal/mol), how can one calculate the strain energy for each compound?

Could anyone also explain whether the trend seen in each series is consistent with expectations based on additivity of ring strain?


texts: Beer's law with a polychromatic light source

texts:
As is well known, Beer’s law (aka the Beer-Lambert law, among others) is predicated on a number of conditions, one of which is that the light source be monochromatic or, as a practical approximation, that the spectral bandwidth of the light source be much smaller than the spectral bandwidths of whatever absorbers are being investigated. For present purposes, a polychromatic light source may be considered to have spectral bandwidth, $\ce S_{source}$, that is not negligible relative to that of the relevant absorbers. The question posed below will deal with what happens when the light source is decisively polychromatic.

Assume a cell path length, b, of 1 cm, and assume a single absorber, having triangular molar absorptivity spectral profile (Fig. 1):

The peak molar absorptivity, $\ce \epsilon_{450 nm}$, is 100 L/mole cm at 450 nm. Assume the absorber concentration, c, ranges from 0 to 0.01 M. In the figure, the absorber’s molar absorptivity spectral profile is modeled as an isosceles triangle. In reality, absorber profiles are often modeled [1, p. 164] as Gaussian, Lorentzian, Voigt, or whatever the underlying physics requires. Here, however, an isosceles triangle is used for mathematical simplicity.

The figure also shows a narrower red isosceles triangle, centered (and having unity transmittance) at 425 nm and having full width at half maximum height (FWHM) equal to 20 nm. This red triangle is the transmittance spectral profile [2, equation 3-60, p. 70] of the light that exits a monochromator, assuming white light of uniform (unity) intensity is incident upon the monochromator and also assuming both 10 nm/mm reciprocal linear dispersion (RLD) and 2 mm slits ($\ce W_{slits}$). With white light incident on the entrance slits of the monochromator, the exiting light has $\ce S_{source}$ = RLD x $\ce W_{slits}$ = 20 nm. Note that $\ce S_{source}$
 is defined here as the FWHM of the spectral profile: this is not the only possible such definition, but it is satisfactory for present purposes. Before proceeding, note that a 0.1 M monochromator typically has something like RLD = 4 nm/mm and 2 mm slits are relatively huge, as slit widths go, so the light source’s profile is polychromatic (and not good at all). Indeed, the FWHM is 20 nm, while that of the absorber is 50 nm.

As always, $\ce T(\lambda) = I_{transmitted}(\lambda)/I_{incident}(\lambda)$ and $\ce A(\lambda) = -log[T(\lambda)]$. If $\ce c = c_{max} = 0.01 M$ and b = 1 cm, then the next figure shows the absorbance (black) and transmittance (red) spectra from 380 to 520 nm (Fig. 2):

If the light source was monochromatic, at 425 nm, a Beer’s law plot would be a straight line with slope = $\ce \epsilon_{425 nm}$ x b = 50 L/mole cm x 1 cm = $50 M^{-1}$.
For absorber concentrations from 0 to 0.01 M, $\ce A_{max} (425 nm)$ = 0.5 at $\ce c_{max} = 0.01 M$.

However, for the light source profile in Fig. 1, the Beer’s law plot will curve downward, as undergrad textbooks like to show in cartoon form, and the absorbance at $\ce c_{max}$ will be less than 0.5.

Question: For the above scenario, with the specified polychromatic source profile in Fig. 1, what is the absorbance at $\ce c_{max} = 0.01 M$?

Hints: 1) Forget about undergrad textbooks for this. 2) There is no added noise or error. 3) The light source cannot be modeled as a pair of monochromatic lines.

Assume the photodetector responsivity is flat from 200 to 700 nm and dark response is zero. There is no detector or preamplifier noise, no digitization error, and no source shot noise. This is idealized in every reasonable way except for the polychromatic source, which, of course, no one would deliberately use.

References:

T.C. O’Haver, “Effect of the Source/Absorber Width Ratio on the Signal-to-Noise Ratio of Dispersive Absorption Spectrometry”, Analytical Chemistry, 63 (1991) 164-169.
J. D. Ingle, Jr. and S. R. Crouch, Spectrochemical Analysis, Prentice Hall, Englewood Cliffs, NJ, ©1988, pp. 70-74.


texts: How does boiling water extract dyes from vegetables?

texts:
Why does boiling water always seem to release and become the colors of whatever vegetables I am boiling?

For example, beet root and red cabbage both vividly color hot water.

I'd assume it's something to do with collisions with water particles breaking down cell walls and releasing a pigment, but how would this work on a physical level?


texts: What are the dangers of melting HDPE and silicone? Is it even possible?

texts:
I've searched the internet and couldn't find a specific answer.
There doesn't seem to be a single recycling company that takes empty silicone tubes (also know as mastic tubes) and recycles them. As a result, here in the UK it goes to landfill. Such a shame and doesn't seem right!

The tube is made from HDPE but is contaminated with the silicone inside it, usually used for sealing windows or bathrooms.

There is a chemical solution available that will strip out the silicone by dissolving it but that doesn't make commercial sense for two reasons;

The cost and time involved
You are left with a chemical to dispose of

Nobody wants these tubes and it has begun to annoy me!

I'm wondering if anyone could advise of the possibility / dangers of simply melting the empty tubes which result in a plastic mix of HDPE and silicone?

Would it work? Could it work?


texts:
How many liters of hydrogen, H2, are needed to react with 10 liters of nitrogen gas in the reaction forming ammonia?

$$\ce{3 H2(g) + N2(g) -> 2 NH3(g)}$$

My try:: Because we have 10 L of nitrogen gas, we have 10/22.4 moles = 0.446 moles of nitrogen gas, and thus need 0.446 * 3 = 1.338 moles of hydrogen gas. As such, we need 2.676 grams of hydrogen gas, or 2.676/0.09 = 29.8 L of hydrogen gas. However this is not correct. Can someone find my problem?

Note: This reaction occurs at STP.


texts:
There are several reports of synthesis of amines from acyl azides via Staudinger reaction with triphenylphosphine.

Are there any reports of Staudinger reactions of acyl azides to amides? If not, are there any reports on reduction of acyl azides to amides? I have found a paper (http://www.tandfonline.com/doi/abs/10.1081/SCC-120014032) that talks about the reduction of acyl azides to amides using zinc and ammonium chloride, but I am looking for some other reactions as well.


texts: Non-halogen intermediate between alkane and alcohol under basic conditions?

texts:
Using organic chemistry I have failed to find a method that doesn't involve halogens (gasseous especially).

Please ignore the enzyme mono-oxygenase, which adds $\ce{O2}$ directly to alkanes to form alcohols.

[edit] Regarding selectivity the reaction should preferably stop at the alcohol stage.

The most promising method I have found involves Boranes, but only works for terminal alkanes. The termial organoborane can then be converted to an alcohol.

I found it using a google search inspired by the answers below: "photochemistry of alkanes."


texts: Uses of Fourier / Laplace transforms in chemistry (apart from spectroscopy)

texts:
I'm just now learning about the Fourier transform, which seems like a pretty useful tool, and I know it has uses in spectroscopy (e.g. FTIR) since that is what Google shows when searching for applications of the Fourier transform in chemistry. Interestingly, I found out that the Laplace transform can be used in
chemical kinetics.
I was wondering if there were any other cool uses for the Fourier/Laplace transform in chemistry?
And if so, any links to resources to learn more about that particular use would be appreciated.


texts: How to get Jmol to automatically determine and display bond order?

texts:
Some molecule file formats do not detail bond order and when I open these formats in Jmol implied (by the valency, of course) double bonds are not shown as double bonds but rather as single bonds. Is there a way to correct this behaviour? I tried to answer this question myself with a "calculate bond order jmol" DuckDuckGo search. It returned:

http://wiki.jmol.org/index.php/Jmol_as_editor
http://www.wikihow.com/Calculate-Bond-Order-in-Chemistry
http://wiki.jmol.org/index.php/Support_for_bond_orders

as the top three results. Not a single one mentioned something relevant. 3 seemed most relevant but it seems to talk about how to specify bond orders manually, not getting Jmol to automatically calculate them.

Bond lengths are shown in this screenshot:

The file opened is http://crystallography.net/cod/2236556.cif which is tianeptine hydrochloride.


texts: Why is tetramethylammonium hydroxide a stronger base than tri- or dimethyl amine?

texts:
Of the following, which compound is the most basic??

  $\ce{Me3N}$
  $\ce{Me2NH}$
  $\ce{Me4NOH}$
  $\ce{NaOH}$

Between 1 and 2, 1 is more basic as the 3 methyl groups would produce a +I effect resulting in better availability of the lone pair than in option 1.

But the book says it is 3. I don't understand why. I do make out that it is ionic, but how does this fact make it more basic than option 1?


texts: How effective is sulfur in detecting mercury vapors

texts: I've read that powdered elemental sulfur will react to the presence of mercury vapor in the air creating red mercury sulfide, and that an open container of sulfur can be used as a means to verify leaks in a container of mercury that's being kept in a storage cabinet. But is the sulfur reaction/color change sensitive enough relative to the permissible levels of mercury vapor that might exist?


texts:
Is negative activation possible? And, in coupled reactions is there any difference?

Because I saw in the paper - Chemical Engineering Science 1996, 51 (11), 2995–2999 - the following conclusion:

  Negative activation energies of reaction have been observed [...]. This unusual phenomenon can be predicted from classical theories, as a competition between two consequences of a temperature increase: greater thermal energies available to overcome the energy barrier represented by the intrinsic activation energy, and less adsorption to form reactive intermediates represented by the heat of absorption.

Does it simply mean that although the energy to overcome the activation energy barrier is there but the rate that products are formed is lower?


texts: What are the limits of analytical chemistry?

texts:
As I understand it, the branch of chemistry dealing with identifying substances present in a sample is called "analytical chemistry". This branch looks vast and complicated, with lots and lots of individual techniques applicable in specific circumstances. I'm hardly even a beginner in chemistry, so it's very difficult to get a good grasp of what can be done with current technology.

So, in general, how well can one identify the substances in a completely unknown sample? Does one need to have at least a vague idea of what's in it?

Differently put, let's say I give you a container with a mixture of ten randomly chosen chemicals from the entire CAS Registry, and suppose they didn't react with each other. How difficult would it be to identify all ten of them?


texts: When an expansion of a system does work on its surroundings, is the sign for work negative?

texts:
This question comes to me from trying to explain the answer $1.67\ \mathrm{L}$ of this question:

A cylinder with a moving piston expands from an initial volume of $0.250\ \mathrm{L}$ against an external pressure of $2\ \mathrm{atm}$. The expansion does $288\ \mathrm{J}$ of work on the surroundings. What is the final volume?


texts:
I know that the NMR signal depends on the static magnetic field strength $ B_0 $ (by Boltzmann equation) and its gyromagnetic factor. While NMR occurs when the RF pulse frequency matches the equation:
$$ \nu = \frac{g}{h}\mu_{n}B_{0} $$
what about its amplitude? Does the amplitude of the RF pulse affect the NMR signal? For example, does it affect the signal strength?


texts:
Is there a formula that shows how the density of water is affected by temperature?

For example, with the speed of sound it can be shown how temperature will affect the speed:

$$V = 331\ \mathrm{m/s} + \left(0.6\ \mathrm{\frac{m/s}{°C}}\right)T$$

Is there a similar formula that relates the density of a liquid to temperature? (in this case, water)


texts: Addition of acid to 3-methyl-2,3-dihydropyran

texts:
When a general acid, H-X reacts with the alkene in an addition reaction, which regiochemistry is expected?

In addition reactions X attaches to the most substituted carbon whilst H bonds to the carbon with fewest alkyl groups. In this case I would believe the third carbon to be the most substituted carbon due to it being bonded to three other carbons. And the second carbon to be where the hydrogen will bond. However, apparently it should be the other way around. And this would be the compound formed:

Why is the second carbon the most substituted in this case? Does it have to do with oxygen being more electronegative and thus it is seen as a higher prioritized substituent?


texts: Explain why alumina-containing zeolites possess chemically active surfaces

texts: I think zeolites possess acid sites that are catalytically active in many hydrocarbon reactions. The pore system only allows molecules that are small enough to enter, hence it affects the selectivity of reactions by excluding both the participation and formation of molecules that are too large for the pores. Is that right or not ?


texts: Procedure for determining the levels of Acrylamide from a cup of coffee

texts: For experimental purposes, I want to determine the level of Acrylamide in cups of coffee. Is there a method that doesn't use spectrometric analysis to determine it as I do not have access to it in the lab. Is Acrylamide a Heterocyclic Amine?


texts: The last time I went to my junior college I remember seeing huge blue colored drums labeled ethyl phthalate. So just out of curiosity I decided to check upon this compound. Wikipedia entry containes some information about it's toxicity and usage, but I couldn't understand that part clearly. Could someone help me by listing the possible uses and properties of ethyl phthalate?


texts: Half-reaction for ammonium nitrate comproportionation into dinitrogen monoxide.

texts:
Ammonium nitrate comproportionates into dinitrogen monoxide in the following reaction:

  $\ce{NH4+ (aq) + NO3- (aq) -> N2O(g) + 2H2O (l)}$

I attempted to write the half-reactions by calculating the oxidation state for nitrogen in the ammonium and nitrate ions, and then finding the electrons needed for each half-reaction.

For example, for the ammonium half-reaction, I noticed that $\ce{N}$ is in a -3 oxidation state in $\ce{NH4+}$ and in a +1 oxidation state in $\ce{N2O}$. I concluded that four electrons must reduce ammonia and wrote the following preliminary equation:

  $\ce{NH4+ (aq) + 4e- -> N2O (g)}$

Which I balanced the elements using standard acidic redox into:

  $\ce{2NH4+ (aq) + H2O (l) + 4e- -> N2O(g) + 6H+ (aq)}$

However, I realized that my chemical equation is not balanced with respect to charge, indicating I have a flawed half-reaction.

What would be the correct half-reactions for this chemical reaction?


texts: D6h symmetry clusters- orbital classification confusion!

texts: I was am simulating high symmetry clusters D6h in several programs such as molcas and gaussian. I understand that the highest symmetry used in these programs is D2h and therefore there would be mixing of the different symmetry representations upon correlating from D6h to D2h. However upon simulating Mn@Si12 cluster, I'm seeing that the silicon atoms in the silicon cage have for all representations: s, px, py and pz orbitals despite there being restrictions according to D2h e.g b3u representation has only px functions and b2u only having py functions. Could anyone please shed some light on this phenomenon?


texts: How does common salt speed up the setting of the plaster of Paris?

texts: We use plaster of Paris (POP) to cast and lift foot prints/tyre prints from the crime scene for evidence purpose. While preparing cast, we follow standardized protocol and add a pinch of common salt to the POP solution. It catalyzes thickening of the POP. I am keen to know chemistry behind it. How does salt react with POP?


texts: How to remove white coating on the seashells after lemon acid and soap?

texts: What is the way to dissolve oxalates? I have tried to clean the seashells with lemon (or citric, as I was corrected) acid and then I washed them with soap (with pH above 10). There is a white coating on the shells now, which disappears when is wet and appears back when is dry. I suspect I accidentially covered the shells with some oxalate. Please help.


texts:
I am doing a general overview of different kinds of dualities present in science. I am quite well versed with the dualities in physics and mathematics. I was searching for dualities in chemistry, biology and other sciences. In that process, I encountered "mechanistic duality" in chemistry. For instance, see [1] and [2].

But I am not able to find a good introduction or description about "mechanisitic duality". It would also be nice if someone can briefly explain what this duality mean. Does someone have clue about its history (who coined it first and for what purpose)? Also, please point me to relevant book/paper which discuss this.

Denmark, S. E.; Su, X.; Nishigaichi, Y. The Chemistry of Trichlorosilyl Enolates. 6. Mechanistic Duality in the Lewis Base-Catalyzed Aldol Addition Reaction. J. Am. Chem. Soc. 1998, 120 (49), 12990–12991. DOI: 10.1021/ja982993v.
Ross, S. P.; Baire, B.; Hoye, T. R. Mechanistic Duality in Tertiary Amine Additions to Thermally Generated Hexadehydro-Diels–Alder Benzynes. Org. Lett. 2017, 19 (20), 5705–5708. DOI: 10.1021/acs.orglett.7b02888.


texts:
To remove the temporary hardness from $5\ \mathrm L$ of $\ce{H2O}$ $5.6\ \mathrm{mg}$ of lime is required. Calculate the degree of hardness due to $\ce{Ca(HCO3)2}$ present in water.

My attempt:

$$
\ce{Ca(HCO3)2 + CaO -> 2CaCO3 + H2O}
$$
Since $5.6\ \mathrm{mg}$ of lime is required, amount of calcium bicarbonate present is $16.2 \times 10^{-3} $.

Molarity = ${16.2 \times 10^{-3}}/(162 \times 5)$

$= 0.002\ \mathrm M$.

This is equivalent to the concentration of calcium carbonate.

ppm of calcium carbonate =
 $ 0.002\times10^{-2}\times100\times10^6\times10^{-3} = 200 $

Therefore degree of hardness is $ 200\ \mathrm{ppm}$.

Is the solution correct?
Also I am looking for an alternative method for solving the problem.


texts: Phase diagram of water using Gibbs free energy instead of pressure

texts:
From my lecture course it was indicated that this is what a phase diagram looks like.

Is this diagram applicable to water? All the ones I can find online seem to use pressure on the y axis as oppose to G. If if it is applicable to water, where is the triple point on the graph? I understand it's where the 3 phase lines intersect but this doesn't appear to occur on this type of graph.


texts: If we have some reaction $\ce{A(aq) + B(aq) -> AB(aq)}$  and right now we have less $\ce{A}$ and $\ce{B}$ then we would have at equilibrium, is there ever a time where the amount of $\ce{A}$ and $\ce{B}$ would overshoot the equilibrium of $\ce{A}$ and $\ce{B}$ if the reaction proceeded without any new sources of energy or reactants. In other words, will the concentrations of $\ce{A}$ and $\ce{B}$ always increase towards their equilibrium concentrations but never actually reach those points or will they sometimes overshoot that concentration a large amount (not just an amount that can be ascribed to chance) but then fall back towards the equilibrium concentration.


texts:
I was reading about Interhalogens in JD Lee and in the book it is stated that (without any reasoning) the reactivity order for few of the interhalogens is :-
$\ce{ClF_3 > BrF_5 > IF_7 > ClF > BrF_3 > IF_5 > BrF > IF_3 > IF}$

$\ce{ClF_3 > BrF_3 > IF_3}$
The above is the order for the interhalogens of type $\ce{AX_3}$ which I can understand by the fact that stability would be directly proportional to the polarisability of the compound. But the interhalogens are more reactive than halogens due to poorer overlaps in the first place and going by that logic the order should be reverse. But here that is not the case, Why is that?

$\ce{IF_7 > IF_5 > IF_3}$
Going by the polarisability logic, this order does not makes any sense.
According to me this may be explained by the steric factors, as the number of fluorine atoms around the central atom increases, repulsions between the substituent atoms increases so much that it’s stability gets affected. But the above statement is just a speculation. So what would be the correct reasoning here?

$\ce{ClF > BrF > IF}$
The polarisability argument should be overcome by the poorer overlap at least here according to me but again that is not the case. Why?

[Here by poorer overlaps I mean, We know that for a strong bond, orbital overlaps should take place between the orbitals having little difference in their energies]
And my last question is it possible to theoretically determine the given below order with basic arguments(that is without any data), I suppose it comes out of net considerations of polarisability, overlap, steric factors.
$\ce{ClF_3 > BrF_5 > IF_7 > ClF > BrF_3 > IF_5 > BrF > IF_3 > IF}$
Tl;dr (A) What is the reasoning for the given below reactivity orders?
1.$\ce{ClF_3 > BrF_3 > IF_3}$
2.$\ce{IF_7 > IF_5 > IF_3}$  3. $\ce{ClF > BrF > IF}$
(B) Is there a way to determine given below order theoretically with basic arguements?  $\ce{ClF_3 > BrF_5 > IF_7 > ClF > BrF_3 > IF_5 > BrF > IF_3 > IF}$
[Note that in the book no specific mentioning has been done that is, it has not been mentioned reactivity with respect to what]
References:-
Concise Inorganic
Chemistry by JD Lee (Fifth edition)


texts: Capillary action only works with glass tubes?

texts: I tried to reproduce the capillary action and measure how high the water rises. So far, I've tried unsuccessfully with a regular drinking straw and a very narrow plastic tube with an internal diameter of about 0.5mm. Does the tube have to be glass for it to work?


texts: Concentrating mixtures of volatile compounds

texts:
My interest is primarily food-related here but I think this is a fairly general chemistry question. Let's say I took some liquid like lemon juice and ran it though a rotary evaporator to get just the volatile compounds. In the case of lemon juice I'd assume I'd wind up with mostly water, and some other volatile compounds (that would smell exactly like lemon juice does). To increase the intensity of this we'd need to somehow remove water.

Similarly a common technique for making extracts is to dissolve volatile compounds of common aromatic foods into alcohol. In case this process left any non-volatile compounds you could certainly use a rotary evaporator. You wind up with a somewhat similar issue where alcohol is the primary liquid.

I'm wondering if it would be possible to concentrate such mixtures so that they contain higher ratios of smell-able volatile compounds to water/alcohol. One thing I've noticed is that most of the characteristic volatile compounds in say lemons have a much higher molecular weight than water or even alcohol. Is there someway to utilize this to like centrifuge out a more concentrated liquid? Are there good methods for either water or ethyl-alcohol specifically?


texts: During my study of aromaticity, I came through this topic of quasi-aromaticity. Can you please elaborate what Quasi aromatic compounds are and how are they designated?


texts:
This molecule has 6 peaks in its proton NMR. I think this is due to the following tautomerisation:

However, I am unsure as to whether this molecule would be chiral, as it can freely interconvert between these two forms, when each form is itself chiral.


texts: What is the pKa of the second ionizable group?

texts:
One compound contains an amino group with $\mathrm{p}K_\mathrm{a}$ of $8.8$, and one other ionizable group with a $\mathrm{p}K_\mathrm{a}$ of $5$ to $7$. To $100\ \mathrm{mL}$ of a $0.2\ \mathrm{M}$ solution of this compound at $\mathrm{pH}\ 8.2$ was added $40\ \mathrm{mL}$ of a solution of $0.2\ \mathrm{M}\ \ce{HCl}$ and the $\mathrm{pH}$ changed to $6.2$. What is the $\mathrm{p}K_\mathrm{a}$ of the second ionizable group?

I am a little confused because I am not sure what to do when the $\mathrm{pH}$ does not equal the $\mathrm{p}K_\mathrm{a}$ of the amino group. I'm thinking since the known $\mathrm{p}K_\mathrm{a}$ of $8.8$ is highest at that point there should be no free $\ce{H+}$.


texts: Material that absorbs only in NIR and emits in visible

texts: This Thorlabs VRC4 card here uses a material that absorbs only NIR and emits in visible. The spec sheets don't list what chemical this is. Do you know materials that show similar emission properties even with weak laser excitation?


texts: Methods: Does failing at intermolecular properties mean the same for intramolecular properties?

texts:
Let us consider the following:

1.) Method X fails at describing intermolecular non-covalent interactions.

2.) Method X excels at describing molecules of type Y.

3.) Method X ___?___ at describing molecules of type Y_1 containing intramolecular non-covalent interactions.

Is there an existing general consensus on number 3? I haven't found an example in the literature yet which would highlight a clear answer to this.

EDIT for clarification:

Example 1: An non-covalent intermolecular interaction would be the interaction of two stacked benzene molecules.

Example 2: A molecule of type Y could be like an amino acid. This molecule has well defined, strong covalent bonds.

Example 3: An organic molecule with a non-covalent interaction occurring between two functional groups.

So... regarding #3, would we expect the method to do well at characterizing a molecule in Example 3, would we expect the method to fail (as it did in Example 1) or is there no general consensus on the matter which is essentially the same as saying, "Just have to try it and see!"?


texts: Which is a better measure of polarising power of a cation?

texts: Recently, I have come across literature stating that polarising power of a cation is proportional to the inverse of the surface area $(4\pi r^{2})$ while some associate it with the charge density of the cation, and thus state that it is proportional to the inverse of the volume $(\frac 43 \pi r^{3})$. I have been wondering which is a better measure of the polarising power. My knowledge of physics is limited so I would like to ask if anyone could kindly enlighten me on the matter.


texts: Why are most hydrocarbons less dense than water?

texts: Why are most hydrocarbons, like alkanes and alkenes, less dense than water?


texts:
I'm currently very desperate to know this. I'm doing an experiment about adsorption/chelation of Cu ions in CuSO4 using banana peels using the UV-Visible spectroscopy. How do I change the pH of 0.1M or 0.05M of CuSO4? My main problem is with making the CuSO4 more alkaline/basic or whatever u call it. My base pH of the CuSO4 is about 4.0 or 4.1. I've tried making a pH 5 and pH 6 buffer solution then adding it to the CuSO4 solution, but so far it's only made it more acidic.
These are the calculations:
pH 5
Weigh 5.10575g of potassium hydrogen phthalate(C8H5KO4)
Dissolve it in a 100cm3 beaker
Transfer the solution into a 250cm3 volumetric flask and fill it with distilled water
Measure 5cm3 of 2M NaOH and add it to a 100cm3 volumetric flask and fill it with distilled water
Add 100cm3 of 0.1M potassium hydrogen phthalate and 45.2cm3 of 0.1M NaOH into a 250cm3 beaker
pH 6
Weigh 3.40225g of KH2PO4
Dissolve it in a 100cm3 beaker
Transfer the solution into a 250cm3 volumetric flask and fill it with distilled water
Measure 5cm3 of 2M NaOH and add it to a 100cm3 volumetric flask and fill it with distilled water
Add 100cm3 of 0.1M KH2PO4 and 11.2cm3 of 0.1M NaOH
But I realised the phosphate buffers will cause a precipitate. So I tried using a citric acid + sodium citrate buffer. I think the calculation was something like 88.5cm^3 of citric acid + 11.5 cm^3 of sodium citrate (or it could be the other way around). But I don't think that was a buffer solution, cus when I added the slightest amount of deionized water, the pH increased. I got it from https://www.sigmaaldrich.com/life-science/core-bioreagents/biological-buffers/learning-center/buffer-reference-center.html#citric2.
Someone please help this is experiment is basically graded, so I'm really desperate.
edit: I made the copper sulfate using CuSO4.5H2O if that helps


texts:
I understand the principles of electrolysis of salts in aqueous solutions, but there are two points on which i am unsure.

At the positive electrode, how can you work out which ions will preferentially donate electrons?
If the formation of hydroxide ions and hydrogen gas occurs at the negative electrode, can hydrogen ions and oxygen gas be formed instead?

If so, what decides which ions are formed?

What happens to the ions formed at the negative electrode? Do they react with the cations that are attracted to the electrode or do they travel to and react with the positive electrode?

For the last question, I believe the latter would be true because if the anions produced at the negative electrode react with the cations that are attracted to the electrode, the cations that are attracted to the electrode would not be available to accept electrons and hence the current would become increasingly restricted until it stops all together. Could someone negate or confirm this reasoning?


texts: What chemicals are present in burnt toast?

texts: I'm planning to do an experiment where I extract burnt toast and test how that affects the growth of mung beans. I know burnt food contains PAHs, but what are some other chemicals present and how would they affect plant growth?


texts: Why did my lemon and penny battery fail?

texts:
I followed instructions in Popular Mechanics publication for making a battery using lemons and pennies but it didn't work. I have a few ideas on why it might not have worked and would like to know which of them are more or less reasonable.

Here is what I did:

I used sandpaper to remove copper from one side of pennies to reveal the zinc core. Supposedly, only pennies minted after 1982 have a zinc core so I made sure to use only such pennies. The instructions call for 5-10 pennies - I did 6.

Deviations from instructions:

I did not thoroughly remove all traces of copper from 2 of the 6 pennies. The amount of copper that was still visible covered less than 1% of the surface.
I used a lower grade sandpaper than the instructions called for.

I cut cardboard discs slightly smaller than the pennies in equal number then soaked them in lemon juice

Deviations from instructions:

the cardboard discs I cut separated into three layers, the outer two layers appeared to be very tightly pressed and minimally absorbent

I made a stack of alternating pennies and lemon-soaked cardboard discs with the copper-side of each penny facing down. On the top of the stack I placed an intact, non-sanded penny then wrapped electrical tape around the stack.

Deviations from instructions:

none that I am aware of

I attached an LED to the top and bottom on the penny stack. I tried both combinations of where to put the positive and negative ends but neither caused the LED to light up.

Why I think it Failed:

By not removing every last trace of copper from the sanded-side of the pennies, I created a kind of short-circuit that discouraged the charges from moving through the stack of pennies.
Since the cardboard was not very absorbent, it might have been particularly porous either and this might have prevented sufficiently free flow of particles between each penny in the stack.
By using a relatively low number of pennies, I guess I set it up to have a relatively low voltage. Maybe I could have overcome problems 1 or 2 if I used more pennies.

I want to know if I my assessment of what went wrong is reasonable and welcome any suggestions of things I might be overlooking.


texts: What happens to the third hydroxyl group in a phosphodiester linkage?

texts:
A phosphodiester bond occurs when exactly two of the hydroxyl groups in phosphoric acid react with hydroxyl groups on other molecules to form two ester bonds.

But what happens to the third hydroxyl group; i.e. why is it an oxygen and not hydroxyl?


texts:
Consider an atom (carbon) with a ground state valence electron configuration of:

$$ \underset{3s}{[\uparrow \downarrow]} \underset{3p}{[\uparrow \vert \uparrow \vert \; \; ]} $$

In some molecules such as carbon tetrafluoride, carbon can "expand" to a more energetic electron configuration similar to:

$$ \underset{3s}{[\uparrow]} \underset{3p}{[\uparrow \vert \uparrow \vert \uparrow ]} $$

Although these orbitals would usually be mixed together and also paired together with the opposite atoms they are attached to.

Are there any cases where the reverse can happen?

For example could phosphorous "contract" from

$$ \underset{3s}{[\uparrow \downarrow]} \underset{3p}{[\uparrow \vert \uparrow \vert \uparrow ] }$$

to

$$ \underset{3s}{[\uparrow \downarrow]} \underset{3p}{[\uparrow  \downarrow \vert \uparrow \vert \; \; ] }$$

Looking at the geometry of p orbitals and taking into account molecular orbital theory I think this is always of non benefit unless possibly the materials are put under external strains such as high pressure or heat.

Also, in the cases of atoms like chromium which are "expanded" by default I'd imagine contraction to the typical state could happen.


texts:
I was wondering how one could test the hypothesis that boric acid behaves not as a Brønsted acid but as a Lewis acid in that boric acid cleaves water molecules as to make hydrogen protons.

rad
Could one run an experiment involving boric acid in heavy water ($\ce{D_2O}$)?

Thus, if boric acid behaves as a Brønsted acid, the concentration of deuterium cation should stay the same, right? Boric acid might release hydrogen protons but those wouldn't affect the deuterium protons, right? Wouldn't heavy water still undergo auto-ionization and create a certain equilibrium concentration of the heavy equivalents of hydronium and hydroxide ions?

And thus, if boric acid behaves as a Lewis acid, couldn't we somehow precipitate the $\ce{B(OH)_3(DO)^-}$, and test whether the precipitate has D rather than H? I.e. introduce sodium chloride into the system and evaporate to dryness. Wouldn't that leave behind a precipitate consisting partly of sodium ion and partly of the borate? On the other hand what would happen to the excess chloride ion?


texts: Why would I not see a reaction between aluminum and tin(IV) chloride?

texts:
I was performing an experiment where I was supposed to construct a modified activity series between certain elements. I decided to use chlorides with the other metals for single replacement reactions so I could compare them all in relation to one another for my modified activity series.

When I placed about one gram of aluminum into about five milliliters of tin(IV) chloride, I was not able to see any reaction taking place. However, aluminum is higher in reactivity on the activity series so I know the aluminum had to react to replace the tin, but why would I not be able to see it?


texts: Calculate the transition dipole moments between the 1s inner shell and the high-lying states of a molecule

texts:
I am trying to calculate the transition dipole moments between the 1s inner shell and the  high-lying states of N2, namely, $<\psi_{1s}|{\bf r}|\psi_{high-lying}>$.

For this, I installed GAMESS (US) and calculated molecular orbitals of N2.
However, I only got HOMO-6 to LUMO+2.
I want LUMO+3, 4, 5... and if possible, 1s.

How can I do this in GAMESS? Or do I need other softwares?


texts: Zwitterions/IEP of glycine at pH 6? (Paradox?)

texts:
I am trying to understand an experiment: Some crystalline, solid glycine was solved in water and a pH=6 was measured (also calculable with $\mathrm{pH} =\frac{1}{2}(\mathrm{p}K_\mathrm{a1} + \mathrm{p}K_\mathrm{a2} = \frac{1}{2}(2.34 + 9.6) = 5.97)$

I have tried to explain the acidic pH-value: Solid glycine is in a crystalline structure — all molecules are in a zwitterionic state. If they get solved in neutral water, the crystal-structure is lost and $100~\%$ of zwitterions are dissolved in the neutral solution. The carboxylic and amino group now act as an acid and base in aqueous solution. The acid reaction of the carboxylic group predominates ($\mathrm{p}K_\mathrm{a1} < \mathrm{p}K_\mathrm{a2}$). Some amino acids are now negative ions, some are still zwitterions.

But now is my question (the contradiction?): pH = 6 is also the isoelectric point IP with the definition, that all amino acids are in zwitterionic state. But according to my theory above, some amino acids have already reacted "away" from the zwitterionic state.

Are there flaws in my reasoning — is my explained "paradox" not true?


texts: Ketone prefix organic chemistry nomenclature

texts: Is there a difference between the prefixes keto- and oxo-?


texts:
I have some colloidal silver that i bought from a shop. It is 18ppm, however, I need a higher PPM and I can't seem to buy it anywhere where I live.
If I boil this colloidal silver, would it make the final concentration of silver go up?
For example, If I had 1 liter of 18ppm colloidal silver, and boiled it until I only had 500ml of colloidal silver, would that mean that I now have 500ml of 36PPM colloidal silver?


texts: Maximum hydrogen atom bonds per a single carbon atom

texts:
I was solving a chemical formula which includes a carbon, oxygen, and hydrogen compound. And it turned out to be something like this:

$$\ce{C_nH_{4n}O}$$

when $n$ is a natural number. So that, at least ostensibly, can be one of these:

$$\ce{CH4O, C2H8O, C3H12O, C4H16O, ...}$$

But a solution attached to it said

  The only compound which has $\ce{C_nH_{4n}O}$ as the empirical formula is $\ce{CH4O}$

so the molecular formula is confirmed as above. So simply my question is this: why is that the only one which makes sense in this situation?


texts: Why doesn't solvent form the major product in SN1 reactions?

texts:
If in a reaction SN1 pathway is followed then after the formation of carbocation the reagent or the solvent molecule can attack to form the product. As the number of solvent molecules are significantly higher than the reagent molecules the solvolysis product should be the major one, but then why is the reagent substitution product given as the major one?

Is is just because we have to 'use' the reagent since it is given to us?


texts: Volume of compressed helium gas needed for FE test on ball valves

texts:
I'm currently doing a case study to find out the exact volume of helium gas required for FE tests on ball valves  regards to the valves' volume and pressure class and the number of helium tanks needed for it (assuming the test is being done at room temperature)
The specifications of helium gas that is being supplied to the test bench is as follow :
Helium 5.5
Purity: 99.9995
Size: X50S
Pressure: 200B

The gas capacity (with regards to the Helium Gas) 8.57NM3
The water capacity. 50L
The dimension of the cylinder tank .1,51M height
The weight of the cylinder tank (with and without the Helium Gas)  Net fill weight 1.51KG. Gross weight vary.
The maximum pressure in which the tank can be operated. Max working pressure 200 Bar
The valve outlet. BS3 Brass

Therefore my question is can the gas law be used to find the volume of helium gas needed for the tests and what are the variables that is needed in finding the volume?
ex: P1 = Valve Maximum Pressure, P2 = Helium Cylinder Tank Pressure, V1 = Valve Internal Volume (has been calculated), V2 = Volume of Helium Gas Needed (required)
Standards for the FE test are:

ISO 15848 Part 1
Shell SPE 77/312

Thank you
Edit:
In simple term, I would like to know what is the volume of helium gas needed to pressurize the valve to reach a certain test pressure?
Given that, the helium cylinder tank has a max working pressure of 200 Bar and a volume of 8.57Nm3. So how much helium gas is needed from this cylinder to pressurize a valve with an internal volume (ex : 0.91594m3) to a test pressure of 19.6 Bar


texts: Building a Voltaic Cell Without Metal Ions

texts:
For an assignment in my Chemistry class we have to build a voltaic cell using materials that are provided to us and that outputs a voltage as close to 0.8v as possible. The list of materials is as follows:

Glass plate
4 filter paper strips

1 ml of the following 1.0M solutions

HCl
NaOH
NaCl
Water

Small metal strips:

Cu
Fe
Pb
Mg
Zn

I originally thought of doing something like this:

This is essentially a small scale version of a 2 beaker voltaic cell with a salt bridge that you see in textbooks. I would attach a multimeter between the Zn and Cu strips and read a voltage.

What I'm confused by however, is that I'm not provided with any solutions of aqueous metal ions, which are required for the half reactions powering this cell to go forward. I know that this has something to do with the HCl and NaOH that I'm provided with, but can't figure out exactly how they factor in.

I've done quite a bit of googling but I'm completely stuck. How would one make a voltaic cell out of the materials I've listed? Thanks for any help in advance.


texts: Why is the equilibrium constant unaffected by a change of the initial concentration?

texts:
In my class, it was taught that the equilibrium constant does not vary with
the intial concentration of the reactants? Why is it so?


texts: About Fe(III) and Fe(II) coordination complexes

texts:
Why does Fe(III) form octahedral coordination complexes if it has 5 electrons in its d-orbitals? I understand that Fe(II) has 6 electrons in its d-orbitals and 6 lone pairs from 6 ligands as the 12 electrons fill up the 3d, 4s and 4p orbitals (18-electron rule, $6+12=18$). However, Fe(III) has 5 electrons and 6 lone pairs is not enough. I know basic crystal field theory and thought that some of the metal-ligand interactions were covalent bonds, but it doesn't add up for both low and high spin states.

Also, do the ligands need to line up with the orbitals form coordinate bonds? I know it sounds counterintuitive since they repel and that's the basis of the crystal field splitting, but how do coordinate bonds form in coordination complexes then?


texts: Does Gallium (liquid or solid) corrode all forms of brass?

texts: I know that it corrodes copper, but does it do the same to all brass or bronze compositions?


texts: Determining order of reaction when concentration of reactant is not given

texts:
Suppose reactant $\ce{A}$ decomposes in an aqueous solution to give $\ce{P}, \ce{Q}$:
  $$
\ce{A(aq) -> P(aq) + Q(aq)}
$$

  Suppose further that $[\ce{A}]_0=0.42\text{M}$, and that $[\ce{Q}]$ was measured as follows (in M):

  \begin{align}
t&=0 &[\ce{Q}]&=0 \\
t&=100 \quad &[\ce{Q}]&=0.101\\
t&=200 \quad &[\ce{Q}]&=0.165\\
t&=300 \quad &[\ce{Q}]&=0.206\\
t&=400 \quad &[\ce{Q}]&=0.239\\
t&=500 \quad &[\ce{Q}]&=0.263
\end{align}

  Using the graph of $\ln [\ce{A}]$ and $\frac 1 {[\ce{A}]}$ vs $t$, determine if the reaction is of order $1$ or $2$.

I know how to solve these kind of problems when I'm given the concentration of $[\ce{A}]$, I just plot the graph and check which one resembles a line more, and the slope gives me the velocity constant $k$.

But here $[\ce{A}]$ is not given. I supposed it would be $[\ce{A}](t)=[\ce{A}]_0-[\ce{Q}](t)$, but I was told that was wrong. Could someone help me out?