texts: Does the starting concentration in a isochoric container depend on the pressure?

texts:
Given is the following reaction of carbonic acid and carbon dioxide:

$$\ce{RCOOH (g) → RH (g) + CO2 (g)}$$

The reaction rate of this decarboxylation was measured in a container with constant volume at $T = \pu{277 °C}$. The following starting pressures $p(0)$ and half-time periods $t_{1/2}$ were measured whereas there was only carbon acid at the beginning.

$$
\begin{array}{lrrrrr}
\hline
p(0)/\pu{mbar} & 20   & 40   & 100  & 150  & 200  \\
t_{1/2}/s      & 95.7 & 47.8 & 19.2 & 12.9 & 9.58 \\
\hline
\end{array}
$$

Problem: Why does this data imply that the concentration of the acid doesn't follow a kinematic of the first order?

Answer: A kinetic of first order would have the same half-time period for different starting concentrations. This isn't given here. So this isn't a kinetic of the first order.

Question: It's clear that a kinetic of first order doesn't depend on the starting concentration. What I don't get is: how do I see that we actually have different starting concentrations? Why should the starting concentration depend on the starting pressure?

My though: We have

$$ c = \frac{n}{V}; \qquad pV = nRT; \qquad V = \text{const}$$

so we get

$$V = \frac{nRT}{p} = \text{const}$$

and from that we get

$$c = \frac{n}{V} = \frac{np}{nRT} = \frac{p}{RT} = \text{const} \quad \to \quad c = \text{const}$$

So apparently, we have the same concentration for different pressures. So how should I see from that data, that the the starting concentration has changed?

I also assumed that we always use the same amount of moles and just change the pressure externally. Maybe they though we change the amount of moles we put in and that changes the pressure, which we then measured?

Edit: I just noticed that sometimes people give the amount of moles of a gas in bars (which is still kind of strange to me), so basically in the units of pressure. I guess that's what's going on here?


texts: Liquids that keeps the lowest temperature for the longer time after being frozen

texts:
I am working on a personal project, however I know nothing about chemistry and I would like to ask you guys for a quick question. I need to use a liquid for my project, which after being put into a freezer will freeze, and will be kept frozen for the most time when taken out of the freezer into room temperatures.

Ideally I would like to know if there is a liquid which can freeze after a couple of hours, and when taken out from the refrigerator it can sustain a temperature of -2 -3 degrees for the longer period, in normal room temperatures. And most importantly it can me used again and again.

Thank you so much guys, I will be looking forward to an answer on this one.


texts: Numerical related to crystallisation of water below its freezing point

texts:
Question:

  There is $16\ \mathrm g$ of pure water in a container at temperature $-20\ \mathrm{^\circ C}$. A small piece of ice is added to start crystallization. Amount of water in container when temperature reaches to $0\ \mathrm{^\circ C}$ is: (assume specific heat of water below $0\ \mathrm{^\circ C}$ is $1\ \mathrm{cal\ g^{-1}\ ^\circ C^{-1}}$.)

My attempt:

I have read this: Liquid water below freezing temperature. So, I understand that the small piece of ice is only added to provide a nucleation site to promote the freezing of water.

But, all physical processes must follow the Law of Calorimetry, right? So, for water below $0$ degrees to freeze, it must first accept heat from somewhere, to reach zero degrees. But, the container is at an even lower temperature, so it won't provide water with any heat (negative temperature gradient). We have also not been given the mass of ice added, so we can't calculate the amount of heat the water will gain from the ice (the latter is at a high temperature than water). The system is isolated, so there is no other possible heat source...

I am apparently at a dead end in this problem. I hope I have put everything in detail and correctly. What is the logical mistake in my thinking? And what is the correct way to approach this problem? Thank you!


texts: 3D Resin Printers - Ventilation & Safety?

texts:
After a year of research and developing my skills in 3D modelling, last week I purchased a 3D printer. I decided a resin printer is most suitable for the applications I am interested in, however I have some concerns about the safety of at-home printing of this kind; particularly when it comes to airborne fumes and particulates.
These printers use UV-curing liquid plastic resin. I wonder if anyone could shed some light on the dangers of these chemicals and what steps should be taken when handling or running a 3D printer of this kind at home? I have seen mixed advice online from hobbyists. Most of the advice concerns direct contact with skin but there appears to be very little discussion about necessary ventilation. For example, I am thinking about building a vacuum-exhaust enclosure...
The type of resin used in these printers:
https://www.3djake.uk/resin
Thanks


texts:
Soda-lime glass is made by melting together soda (sodium carbonate), lime (calcium oxide), dolomite (calcium magnesium carbonate), silica (silicon dioxide), alumina (aluminum oxide), and small quantities of other compounds. Wikipedia says this is done in a furnace at "up to" 1675 °C. Many of the carbonates decompose at lower temperatures, 650 °C for dolomite and 851 °C for soda. However, soda-lime glass begins to soften at 700 °C.

Given the high decomposition temperature of carbonates like soda and dolomite, which is close to and sometimes higher than the temperature at which soda-lime glass begins to soften, one might think that there is a potential for some carbonate to remain dissolved in the glass. This is perhaps supported by the fact that silicon and carbon are both Group IV elements and could share spaces in the same lattice structure.

However, I haven't been able to find a quantitative analysis of soda-lime glass which measures oxidized carbon content. Is this because it's difficult to measure, or because no one in the glass industry cares, or because it's actually very close to zero?


texts: How to compare dipole moment in thiophene, furan, and pyrrole?

texts:
This is what I found (source):

I wonder about several things here.

First, why is tetrahydrothiophene's dipole moment bigger than that of tetrahydrofuran, when considering that tetrahydrofuran has an atom of stronger electronegativity?

Secondly, why thiophene has weaker dipole moment when the S atom has larger p obitals, and therefore, has weaker conjugation ability than O to aromatic ring. The result seems that S in thiophene has better conjugation effect. (that's why it has less stronger dipole.) and I don't seem to explain why.

So what are the reasons for these dipole moment orders?


texts: Why is KI oxidized by H2SO4, whereas NaBr isn't oxidised?

texts: My textbook says that alcohols react with sodium bromide and sulphuric acid to form the corresponding alkyl bromides. At the same time they also mention that sulphuric acid mustn't be used with potassium iodide ($\ce{KI}$), because $\ce{HI}$ formed would be oxidized to $\ce{I2}$. Won't $\ce{HBr}$ formed from $\ce{NaBr}$/$\ce{H2SO4}$ oxidise to $\ce{Br2}$?


texts: How can sodium chloride melt ice or keep it frozen?

texts:
In European countries, they use $\ce{NaCl}$ or $\ce{KCl}$ to melt ice during the winter season.
In Asian Countries, they use $\ce{NaCl}$ to keep the ice without melting, for example in ice cream and beer boxes.

I asked my chemistry teacher about this and his answer was,

  when you add ions to the ice, its melting point goes (i.e. freezing point of water) to -9 to -19 degree Celsius, depending on the amount of ions. The reason behind that is, when water becomes ice its water molecules re-arrange to specific shapes (see the link for the video at bottom). After we put ions to it, ions disturb that shape as they come in-between the water molecules. If water wants to be ice again, it should be like -9 degree Celsius because of these ions disturbing them to rearrange as a solid.

I also asked my Physics teacher about this and his answer was,

  When we put salt into water, its temperature goes down to somewhere around $\pu{-6 ^\circ C}$, so that it takes more time to come to $\pu{0 ^\circ C}$ and begins melting

Link to the videos are as follows,

Salt melts ice (YouTube)
Salt reduces the temperature of ice (YouTube)

Could you give me a correct explanation for this question?


texts: Can you dissolve latex balloons to remold into other latex objects?

texts: I want to take balloons from the dollar store and dissolve, then reform them into complex shapes (like a human head) balloons. Is this possible?


texts: Enzyme Kinetics - Given Km find substrate concentration at a certain velocity

texts:
From what I understand about the Michaelis Menten Model

Km defines the amount of substrate required to reach half-saturation.
1/2 Vmax corresponds to Km on the x axis
Generic formula is v = Kcat [ES] [S] / (Km + [S])

Given Km and the desired velocity in terms of reaction efficiency, can one just plug in Km into the equation and get a relational expression with [S] on one side?

Or do you manipulate the 1/2 Vmax expression?


texts: Does Magnesium metal react with carbonic acid?

texts: I use rainwater in my house for my water supply.  I collect the water in plastic lined tanks.  Some of my piping at home is copper, and I have blue stains in my shower, because I think the copper from my pipes is being dissolved by the carbonic acid in the rainwater.  I'm planning to hang magnesium rods into my rainwater tanks, in the hope that these rods will react with the carbonic acid instead of my copper pipes.  Does that make sense?


texts: Nomenclature of Organic Compound from Condensed Formula

texts:
I am just unable to name $\ce{C6H5CH2C6H5CH2C6H5}$ using IUPAC nomenclature.
I tried searching online however I couldn't find a name for it.


texts: Can you purify a metal oxide with a laser?

texts:
Is there any metal oxide (like aluminum oxide, titanium dioxide etc.), that can be put into a vacuum and hit with a heat source, like a laser and be converted into pure metal with a slightly weaker vacuum having oxygen in it?
From my understanding pure metals tend to oxidize at higher temperatures, however, since "nature hates a vacuum", is it possible to use heat to do the opposite process by providing enough energy to break it's chemical bonds and then the oxygen joins the vacuum leaving the metal behind?
If this is impossible. Is there another way to use a laser to purify metals? If heat doesn't do the trick even in a unique environment, perhaps is it possible to focus ionizing radiation to essentially perform electrolysis on it?
Again, this might not work. So one last idea. For example, aluminum oxide and titanium dioxide are dielectrics. If you were to hit one side with an electron beam from a cathode ray tube to negatively charge one surface and use ionizing radiation on the other side could you then create a chemical reaction to purify the metal?


texts: Second order Jahn-Teller effect for d0 complexes

texts:
I was wondering why the second order Jahn-Teller effect is also said to happen for many d0-systems? It makes sense to me that due to relativistic effects and the stabilization of the s-Orbital and destabilization of the d-orbitals the energetic gap between the let's say eg in an octahedral complex and the above laying unoccupied a1g s-orbital becomes small enough that, for the right amount of electrons filled into the d-orbitals a mixing of both states is of some advantage leading to a second order Jahn-Teller effect like in Hg(II) compounds. But why does it also happen to d0-complexes?

My suggestion would be that we cannot discuss any field splitting in the first place. So first of all, how would any distortion here give us an energetic advantage and then also we would have to take the nephelauxetic effect of the host or ligand more into consideration if we do not consider a real crystal field splitting. I don't really know where a methyl ligand would be considered in the nephelauxetic series (since some heavy transition metal methyl complexes form trigonal prismatic complexes rather than octahedral ones, which is often explained with a second order Jahn-Teller effect) but if I consider some covalency in this metal-carbon bond then it may shift the d-orbitals down enough so they could perhaps mix with the lower occupied p-Orbitals. So that perhaps the mixing is not between occupied d- and unoccupied s-orbitals but between occupied p- and unoccupied d-Orbitals.

EDIT:

I was reading an article on the second order Jahn Teller effect yesterday and found the following line:

I am not sure if I got all those rules correctly but it seems like I have to consider the product of both states and the product has to be of the same symmetry. If I think about the next low lying occupied orbital in an octahedral environment it would be the filled t1g Orbital. So This would mean I have to consider a t1g and t2g mixing here. I have no clue about those irreducible representations and point groups but from the tables you can find on the net I found that a multiplication of T1 and T2 in Oh point-group would end up in an A2 + E + T1 + T2. As this contains both T1 and T2 I guess it will somehow obey those rules.

Perhaps someone with more experience in symmetry and character tables might have suggestion about this.


texts: Why is iron pentacarbonyl known, but iron(III) hexacarbonyl is not?

texts: Why is the neutral complex $\ce{[Fe(CO)5]}$ known, but the cationic carbonyl complex $\ce{[Fe(CO)6]^3+}$ is not known?


texts: Can we interpret the "extent of reaction" as the number of reactions that happened?

texts:
Consider this reaction:
$$\ce{\alpha\ A + \beta\ B -> \omega\ C + \delta\ D}$$

Where $\ce A$ and $\ce B$ are the reactants, $\ce C$ and $\ce D$ are the products, and $ \alpha, \beta, \omega, \delta$ their respective stoichiometric constants

We can then define the extent of reaction at instant $t$ as: $\xi (t)$.

My question is: can we interpret the extent of reaction as the number of reactions that happened at an instant $t$ considering that say, for reactant $\ce A$ at instant $t$: $$n_{t}(\ce A) = n_{i}(\ce A) - \alpha\times \xi(t)$$


texts: is there any hydrophobic material to be used on paper cups?

texts: Is there any bio degradable hydrophobic material that is not poisonous and easy to spray up on paper cups?


texts:
Actually this is going to be a list of interconnected questions. Please bear with me.

Wikipedia article on cyclodextrin (CD) says that it is hydrophobic from inside.

(1) How is it hydrophobic when there are so many hydroxyl groups on the interior surface ?

(2) This image
    labels the interir cavity as apolar rather than hydrophobic. I guess
    the apolarity is because of mutual cancellation of the dipole
    moments.
Am I right on this?

In any case I don't understand how the cavity excludes water.

There are reports on trapping organic substances such as naphthalene, toluene and crude oil in the CD cavity. Another report says that nitrosamime is trapped in CD by interacting with the hydroxyls.

(3) How does this trapping exactly occur ?

(4) Do the hydroxyls play a role in restricting the diffusion of the trapped organic molecules out of the cavity ?

All of this, I started investigating because of a recent news about an alcoholic beverage in powder form- palcohol. Initially I didn't believe it but later I found that alcohol is absorbed in CD to make a dry powder.

(5) What prevents alcohol from adsorbing on the exterior surface and not make the powder sticky ?

(6) Other studies say that there is a 1:1 ratio of trapping but palcohol claims that it is 58% alcohol by weight. Even this old patent says that CD absorbs a lot of alcohol. How does that happen ? In all it seems that CD behaves differently with different molecules.


texts: Can "Common Ion Effect" suppress the dissociation of water molecules in acidulated water?

texts:
$$\begin{align}
\ce{H2O &<=> H+ + OH-} \\
K &= \frac{[\ce{H+}][\ce{OH-}]}{[\ce{H2O}]} \\
\ce{H2SO4 &<=> 2H+ + SO4^2-}
\end{align}$$

In acidulated water water dissociates into its respective ions(though the dissociation is very less) and simultaneously acid dissociates into its respective ions.

Now as the acid (I have taken $\ce{H2SO4}$ here) also dissociates to give $\ce{H+}$ ions. So the $\ce{H+}$ ion concentration increases which in turn affects the equilibrium of $\ce{H2O}$ and favours the backward reaction forming $\ce{H2O}$ back. So can we say common ion effect has suppressed the dissociation of $\ce{H2O}$?

And if this is the case then why do we use acidulated water while performing the electrolysis of water? (I mean the common ion effect can suppress dissociation of water and we would get less $\ce{H+}$ and $\ce{OH-}$ ions in the medium which would lead to a lower yield if $\ce{H2}$ and $\ce{O2}$ gas.)


texts: Isn't water a Lewis base in the ammonia–water reaction?

texts:
Exactly one of these statements is false. Which one?
(a) When ammonia dissolves in water, the latter behaves as a Lewis base.
(b) The conjugate acid of $\ce{H-}$ is $\ce{H2}.$
(c) Boric acid is a monobasic acid.
(d) Ammonia behaves as an acid when it reacts with sodium metal to give sodamide and hydrogen.

The key says (d) is the false statements. How? I think (a) is the one.
(d) $\ce{2NH3 + 2Na -> 2NaNH2 + H2}$
The ammonia here loses a proton, which is characteristic for acids. In addition, it attaches to the electropositive sodium.
(a) On the other hand, when ammonia dissolves in water:
$\ce{NH3 + H2O <=> NH4+ + OH-}$
Ammonia gains a proton, which is characteristic for bases.


texts: What chemicals are often confused for different chemicals?

texts:
Recently I asked a similar question on Chinese SE: Why would Antimony (Sb) and Aluminum (Al) be confused?

It seems, though, that this is by no means a Chinese phenomenon.

The Wiki page for Tin foil mentions that:

  aluminium foil, [...] is still referred to as "tinfoil" in many regions.

What other chemicals are often confused for different chemicals?

I'm especially interested in things that have retained their incorrect names.


texts: Dipole moment - calculation of percentage ionic character

texts:
Question: The dipole moment of $\ce{HBr}$ is $2.60 \times 10^{-30}$ and the interatomic spacing is $1.41$. What is the percentage ionic character of $\ce{HBr}$?

What I know is that the percentage ionic character is observed dipole moment divided by calculated dipole moment $\times\ 100$.

The calculated dipole moment is $\textrm{charge on electron} \times \textrm{radius of molecule}$.

However, how would I convert interatomic spacing into radius?


texts:
My book says water has approximately $\pu{3.35E28 molecules/m^3}$  and that only a small part of water molecules are dissociated to $\ce{H+}$ and $\ce{OH-}$ ions and that the approximate amount of ions of each sign is $\pu{6E19 ions/m^3}.$

I am trying to prove the last part. I thought I could used the ionic product of water

$$[\ce{H+}][\ce{OH-}] = \pu{1E-14},$$

so that in neutral conditions

$$[\ce{H+}] = \pu{1E-7 ions/L} = \pu{1E-4 ions/m^3}.$$

What am I doing wrong or how should I proceed?


texts: Hydrolysis of transition metals' halides?

texts:
So, it's a relatively common known solubility rule that any hydroxide with a cation not in the first two groups is basically insoluble. So supposing we have a transition or post-transition metal $M$ and say it forms a charge of $n+$ (so it's cation is $\ce{M^{n+}}$) why would $\ce{MX_n}$ (where $\ce{X}$ is a halide) remain in solution? Why doesn't the following reaction occur?
$$
\ce{MX_n(aq)} + n\ \ce{H_2O(l)} \rightarrow \ce{M(OH)_n(s)} + n\ \ce{HX(aq)}
$$
My thought was that perhaps this reaction does occur, but just very slowly and not fast enough for the $\ce{M(OH)_n}$ to precipitate in noticeable amounts. However, I don't really know and this is just a guess. Could someone explain to me why this doesn't happen?


texts: ELI5: What is the effect of ultrafine Teflon (PTFE) particles in rats and mice

texts:
I am attempting to research the results of case studies regarding polytetrafluoroethylene [PTFE] (commercially known as Teflon). More specifically I am attempting to make sense of this Abstract on Acute pulmonary effects of ultrafine particles in rats and mice. Not being a chemist I'm having a hard time understanding the results and hoping someone can explain in laymens terms. More specifically, the abstract mentions;

We used ultrafine Teflon (polytetrafluoroethylene [PTFE]*) fumes (count median diameter [CMD] approximately 18 nm) generated by heating Teflon in a tube furnace to 486 degrees C to evaluate principles of ultrafine particle toxicity that might be helpful in understanding potential effects of ambient ultrafine particles. Teflon fumes at ultrafine particle concentrations of approximately 50 micrograms/m3 are extremely toxic to rats when inhaled for only 15 minutes.

That seems straight forward enough. They heated up Teflon in a tube, and made rats inhale it, who subsequently died. Then it goes on to say;

We found that neither the ultrafine Teflon particles alone when generated in argon nor the Teflon fume gas-phase constituents when generated in air were toxic after 25 minutes of exposure. Only the combination of both phases when generated in air caused high toxicity, suggesting the existence of either radicals on the particle surface or a carrier mechanism of the ultrafine particles for adsorbed gas-phase compounds.

This is the part thats unclear to me. The Teflon particles alone, I think means the compound before they heat it, but what is the 'fume gas-phase when generated in air'? How is that different then the fumes they made the rats inhale (from which they died after 15 minutes)? What does the 'combination of both phases when generated in air' mean?

Aging of the fresh Teflon fumes for 3.5 minutes led to a predicted coagulation resulting in particles greater than 100 nm that no longer caused toxicity in exposed animals.

How would coagulation affect the toxicity of the fumes? Does it change the chemical structure of what the animals inhale somehow making it less toxic? Naturally speaking, I would assume 'more' particles would result in higher levels of toxicity, not less.


texts: What electrodes to use to minimise corrosion during water electrolysis?

texts: I did the $\ce{H2O}$ electrolysis experiment a few times, but every time a huge amount of the oxygen reacted with its corresponding electrode. What material should the electrode be made of in order to maximise the amount of oxygen I get?


texts: Why does nucleophilic substitution of a haloalkane with ammonia produce ammonium, not a hydrogen halide?

texts:
For example, $\ce{CH3CHBrCH3}$ reacts with $\ce{:NH_3}$ to make $\ce{CH3CH(NH3^+)CH3 +:Br-}$,$$\ce{CH3CHBrCH3 \rightarrow CH3CH(NH3^+)CH3 +:Br-}$$then reacting again with $\ce{:NH_3}$  to make $\ce{CH3CH(NH2)CH3 +:Br^- +NH4^+}$:

$$\ce{NH_3 + CH3CH(NH3^+)CH3 +:Br- \rightarrow CH3CH(NH2)CH3 +:Br^- +NH4^+} $$

Question: why does the last step not produce $\ce{CH3CH(NH2)CH3 +HBr}$? That is, why is Ammonia a better nucleophile than the halide ion, despite having a lower partial negative charge (the halide has a $-1$ charge)?

Edit: a suggestion made by a teacher is that my proposed step does in fact happen, it's just that it occurs as an intermediary to the last step.  Apparently, it's very favourable to have a Hydrogen Halide and Ammonia acid-base reaction. Is he correct, and if so, why is this?


texts:
I was looking up the Lennard-Jones parameter $\sigma$ (which, to my understanding, is a measure of molecular size) when I was surprised to discover that the value for the $\ce{N2}$ molecule (3.667 Å) was slightly lower than the value for the $\ce{CH4}$ molecule (3.78 Å). It's my understanding that $\ce{N2}$ molecules are significantly larger than $\ce{CH4}$ molecules, and this is exploited in, for instance, molecular sieves.

My question: is $\sigma$ a reasonable measure of mean atomic radius? And if it isn't, what is a good measure of molecular size, with which I can compare molecules?


texts:
I went and bought a bottle of Fanta and some Mentos to replicate the famous youtube videos of the big fizzy reaction.

The result was dismal, it weakly foamed up and dribbled over the edge.

I tried again with Pepsi Max and had a spectacular result (that the kids loved).

I wondered if the carbonation of the drinks was what impacted the difference in reaction.

My question is: Is the variation in carbonation of soft drinks the variable that affects the effectiveness of the mentos reaction?


texts:
I understand rust.  Fe + H20 → OH- → Fe(OH)2 or 3 and/or FenOm
I understand rust prevention and steels that are resistant to rusting.  Trying to google this question gives thousands of answers on prevention.
But what I'm interested in is how to force steel to rust.  And not in an artsy way, so my steel stuff looks weathered and cool (these are the other thousands of search results for forcing iron/steel to rust).  I want to dispose of steel by turning it into iron oxide.  I don't actually really want to do this since it's a lot easier to just landfill or recycle, but I thought of it as an alternative and realized it's really not that easy.
The trouble seems to me that the passivation layer stops rust from completely going completely through the metal.  Can this be forced by running active corrosion circuit in reverse, or will the equation still slow to a crawl once a layer of rust builds up on the surface?


texts: For Penicillin Binding proteins, why is the Enzyme-peptide complex less stable than an enzyme-β-lactam complex?

texts:
I'm trying to figure this out. I cannot find any publications that go into good detail about the chemistry of PBP inhibition by β-lactam antibiotics.

PBPs cross-link adjacent pentapeptides to form peptidoglycan. My understanding is that in most bacteria, this pentapeptide has a terminal D-Ala-D-Ala dipeptide. The enzyme removes the terminal D-Ala and forms a D-Ala-Enzyme complex, where the enzyme is linked to the rest of the peptide via ester bond to the D-Ala.

However, when PBPs bind to β-lactams, they also for a β-lactam-ester-enzyme complex. However, this complex is more stable so the β-lactam remains in the active site. Why? What's different about the β-lactam ester? Or is it perhaps steric bulk that prevents the enzyme from being freed?

Any good publications are also very welcome.


texts: I'm a high-school senior who has just taken the AP Chemistry exam and my teacher has just assigned me an end-of-year project exploring whatever aspect of Chemistry I want. I really enjoy computer programming as well (took the AP last year) and do it a significant amount in my free time, so I was considering finding a Chemistry project that involves some coding or computer modeling (or anything having to do with computers). Could anybody recommend some topics to check out? (I looked at molecular dynamics simulations, but a lot of that stuff contains multivariable calc./quantum mechanics, which might be a bit much).


texts: If I have a mixture of glucose and fructose in aqueous solution, what is the simplest method to separate them? Heating to 110 °C to melt only the fructose would probably work theoretically, but this would cause a huge mess.


texts: Deperoxidation of ethers via alumina: what happens?

texts:
I was reading about the procedures for the removal of peroxides from ethereal solvents, and a procedure which seems to have survived to our days is filtration through a column of "activated alumina" (which, if my understanding is correct, is alumina in its "gamma" form).

What I was wondering is: what happens to alumina? My guess is that it could form a sort of stable complex with (hydro?)peroxides, just like urea or carbonates do.
Yet, I couldn't find an explanation.

If a complex is formed, how stable is it? For instance, if the same alumina employed was dried, either via evaporation at room temperature, or at high temperature in an effort to obtain, again, its gamma form, would it decompose violently? Or maybe would it release oxygen, or gaseous peroxides?

And, if alumina has to be handled with care after use, is there a way to dispose it safely, or (better) to "reduce" it, maybe making it usable again for the same process?


texts: Di-alpha-halogenation of ketones in acidic medium

texts:
I was studying alpha-halogenation of ketones from LibreTexts Chemistry,

  Under acidic conditions the reaction occurs through the formation of an enol which then reacts with the halogen${^1}$.

1) Protonation of the carbonyl

2) Enol formation

3) SN2 attack

4) Deprotonation

It also says (look at the highlighted text):

Overreaction during base promoted α halogenation

  The fact that an electronegative halogen is placed on an α carbon means that the product of a base promoted α halogenation is actually more reactive than the starting material. The electron withdrawing effect of the halogen makes the α carbon even more acidic and therefor promotes further reaction. Because of this multiple halogenations can occur. This effect is exploited in the haloform reaction discussed later. If a monohalo product is required then acidic conditions are usually used${^2}$.

Why can't we just reprotonate the monohalogen in the same way as the initial ketone to form a dihalo compound?

Referance

${^1}$:https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%3A_Organic_Chemistry_(McMurry)/Chapter_22%3A_Carbonyl_Alpha-Substitution_Reactions/22.03_Alpha_Halogenation_of_Aldehydes_and_Ketones

${^2}$:https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%3A_Organic_Chemistry_(McMurry)/Chapter_22%3A_Carbonyl_Alpha-Substitution_Reactions/22.03_Alpha_Halogenation_of_Aldehydes_and_Ketones


texts: Last steps of mechanism of Swern Oxidation

texts: My question is regarding Swern oxidation. Why is the methyl group of the DMSO deprotonated and not directly the red hydrogen atom of the R2-CH-O bond deprotonated? Shouldn't it be that oxygen more electronegative (stronger -I effect) than sulfur and shouldn't that make that corresponding hydrogen atom more acidic? Or is it perhaps that sulfur has a positive charge and therefore acts as a stronger electrophile that attracts the electrons from carbon and therefore its hydrogen groups are more acidic?


texts:
2 is the least basic as the lone pair is involved in aromatizing the ring
1 is the maximum basic as one of the lone pairs is used to aromatize the ring and the other lone pair is available
but how do we distinguish between 3 and 4
the options are:
a.1>3>4>2
b.3>2>4>1
c.4>3>2>1
d.3>4>2>1
by the above discussion we can make out that the answer is a.
but how to distinguish between option 3 and 4. how can we say that 3 is more basic than 4.


texts: Is the SN1 reaction faster with an axial or equatorial leaving group?

texts: Why does compound 1 undergo the $\mathrm{S_N1}$ reaction faster than 2 even though both proceed via the same carbocation intermediate?


texts: Which rings of this heterocyclic compound are aromatic?

texts:
I am wondering which of the inner two rings of this compound are aromatic?

I know the rules for aromaticity. But this case is difficult for me.

Regarding the smaller ring, I guess the sulfur contributes one lone pair of its valence electrons into the system. This means from the nitrogen (in the 5-ring) only one electron is needed for the π-system (with 6 electrons). But this nitrogen atom has only one lone electron pair, thus one of the electrons would not be part of the  π-system of the smaller ring. However, this nitrogen atom in the 5 membered ring is also part of the 6-ring and there it could share both of its free electrons to this larger ring. Then the second nitrogen which is only in the 6-membered ring could contribute one electron only to the aromatic system, and thus having a happy free lone pair left.

What do you think of that? Which rules, logic or reasoning can confirm this? And isn't it a problem that the first nitrogen shares one electron with the 5-ring and the two with the 6-ring?

Also, is there software which can predict this reliably? I haven't found anything so far.


texts:
Are molecules with bond orders less than one stable? My professor commented that they were "barely alive" but what does he mean, scientifically?

I know that molecules with fractional bond orders greater than one can exist - i.e. nitrogen oxide has a bond order of 2.5 (through MO calculations) and it exists just fine.

So are molecules with fractional bond orders below one just very unstable?


texts:
Sulfur and oxygen belong to the same group. Sulfur has a vacant d-orbital while oxygen has no vacant d-orbital.

What does having "no d-orbital" mean? Orbitals are just the spaces around the atom. How can you say that there is no space around the atom which makes the d-orbital?


texts: How are neutral amines effective bases in organic chemistry?

texts:
I have found it to be rather strange that neutral amines, such as triethylamine  or DIPEA, find applications in organic chemistry in deprotonating alcohols or even α-carbonyl compounds. Amines are basic but they aren't really that basic, compared to negatively-charged hydroxides or alkoxides. According to Wikipedia, the $\mathrm{p}K_\mathrm{a}$ (in water) of the conjugate acid of triethylamine is $10.75.$ The same values for alcohols are in the range of $16 - 18.$ For water, it is $14.$ Thus, hydroxides and alkoxides are superior alternatives to these amines.

My motivation for asking about this is that I recently encountered a question in my school chemistry course on why the protection of alcohols with $\ce{MOMCl}$ uses large bulky amines to deprotonate the alcohols, rather than using hydroxides. The answer given was that hydroxides would not be able to deprotonate the alcohols to a significant extent as alcohols are not acidic enough. I find this answer very strange and inconsistent with what I know since as shown by the data above, amines are less basic than alkoxides and hydroxides.


texts: How can the free amino acid B be enantioslectively synthesitzed?

texts:
I would like to know how this reaction actually works. I think its an ring metathesis, espececially with the Grubbs catalysator II. But I dont know how to this reaction examole really works especially with respect to enantioselectivity.
May anyone help?


texts: Thionyl Chloride and enols, carboxylic acids, alcohols

texts:
\begin{align}
\ce{Propanol + SOCl2 &-> Expected~ alkyl~ halide~ product}\\
\ce{Propanoic~ acid + SOCl2 &-> Expected ~acid ~chloride ~product}\\
\ce{Acetone ~enol + SOCl2 &-> doesn't~ work ~in~ the ~expected ~manner}\\
\end{align}

My prof says the $\ce{SOCl2}$ only works on $\ce{sp^3}$ substrates.

But ... both propanoic acid and acetone enol involve an $\ce{sp^2}$ carbon bound to an alcohol group ... why does $\ce{SOCl2}$ work in one case but not in the other?

I think it instead has to do with the nucleophilicity of the electrons involved with oxygen ... the mechanism starts with electrons associated with oxygen attacking thionyl chloride. A regular alcohol has an oxygen with lone pairs that aren't fairly "free," so to speak. An carboxylic acid has resonance donation enhancing the nucleophilicity of one oxygen's lone pairs. In acetone, however, there is no resonance donation ....... (inductive donation, sure).

So does the $\ce{sp^2}$ vs. $\ce{sp^3}$ explanation hold water?


texts: Validity of Henry's Law for an Oxygen/Bitumen System?

texts:
Henry's Law is for a gas dissolved in a liquid and states P = kC where P is the partial pressure of the gas above the solution and C is the concentration of the gas dissolved in the liquid. The k is a "constant", that is, it is independent of P, C and time but depends on the type of gas and the type of liquid. According to Pickover, page 184 (reference below), Henry's Law assumes:

A1.  the gas/liquid system has reached equilibrium, and
A2.  the gas does not chemically react with the liquid, and
A3.  the concentration of gas in the liquid is low, and
A4.  the gas pressure is low.

I would be grateful for any help in answering the following:

Q1.  Is the list of assumptions, A1 to A4, correct and complete? I have no reason to doubt it but I would like to confirm it.

Q2.  Some authors (e.g. Dickinson E.J., Road Materials and Pavement Design, 2000, 1(3), 255-280) have applied Henry's Law to the diffusion of oxygen in air at atmospheric pressure into bitumen which is a semi-solid at room temperature. Is there any experimental evidence that Henry's Law can be extended to such a system?

Reference
Pickover, C., "Archimedes to Hawking", Oxford University Press 2008


texts: Variational method: Hydrogen atom ground state in STO-3G basis expansion

texts:
I computed numerically the ground state energy of hydrogen by variational procedure, firstly expanding the wave function over the s-wave basis set STO-3G
$$\psi(r)=\sum_{i=0}^3 C_{i} e^{-\alpha_ir^2}$$
and then solving the generalized eigenvalue problem (in matrix notation)
\begin{equation}
\textbf{HC}=E\textbf{SC}
\end{equation}
As output I have all 3x3 matrices. $E$ is a diagonal 3x3 matrix and my eigenvalue is the smallest of the three on the diagonal.
My question is: what do the other two elements in the $E$ diagonal represent?


texts: What is the mechanism of the reaction of a ketone with sodium nitrite/ hydrogen chloride?

texts:
What is the mechanism of reaction of a ketone with $\ce{NaNO2/HCl}$?
Can $\ce{NaNO2/HCl}$ be considered as freshly prepared $\ce{HONO}$ here? I am confused about how the reaction will proceed.


texts: What causes the turbidity when preparing Fenton's reagent?

texts:
New guy, please be gentle. I might ask questions not according to conventions, I am not a chemist nor do I study chemistry. Feel free to adapt the question and the tagging.

I am preparing a solution for Fenton's reagents according to [1], mixing 0.750 g $\ce{FeSO4 * 7 H2O}$ (blueish green, cyan almost) to 50 ml deionized (milli-q) $\ce{H2O}$ ([1] uses a slightly higher concentration, but we adapted it according to another publication). This solution needs to be adjusted to $\mathrm{pH}~3$, which, according to [1], can be done with $\ce{H2SO4}$. Now, even if I adjust the solution to well under $\mathrm{pH}~3$, let's say $\mathrm{pH}~1.5$, I still get fallout (presumably a ferrous(III) compound) and a generally turbid solution.
I don't understand what might be falling out and why the solution is turbid in general. What might be happening here? Is the solution somehow reacting with the surrounding air? Could it be further reacting with the water?

2. Fenton’s Reagent
This reagent has two components: $30\%$ (v/v) $\ce{H2O2}$ with an iron catalyst. The catalyst solution was composed of 20 g of iron(II) sulfate heptahydrate in 1 l of filtered RO water. Tagg et al.(34) tested this reagent within the context of extracting microplastics from wastewater. The authors identified this as the optimum concentration. The catalyst solution was adjusted to $\mathrm{pH}~3.0$ using concentrated sulfuric acid.

References

Hurley, R. R., Lusher, A. L., Olsen, M., & Nizzetto, L. Validation of a method for extracting microplastics from complex, organic-rich, environmental matrices. Environmental science & technology, 2018.


texts: What is the phase transformation temperature anatase to rutile phase in tin dioxide(SnO2)?

texts: Usually people discuss only pressure dependent phase transformations in case of either tin dioxide or titanium dioxide. It would be nice if someone gave the phase diagram for tin dioxide.


texts: Which white powders form acids when mixed with water?

texts:
I have a mystery acid which isn't citric, boric, or oxalic acid. When mixed with water, it smells pungent, like hydrochloric acid--though I haven't compared them side by side.

Which other white powders form a strong acid upon being combined with water? Is there any powder that decomposes into HCl when mixed with water?

(Note: the mystery acid was sold as part of a set, along with sodium chlorite, for generating chlorine dioxide for use in aquariums.)


texts: Acidity of 2-sulfopropanedioic acid in water

texts:
Sulfuric acid is a strong acid ($\mathrm{p}K_\mathrm{a}$ value below that of $\ce{H3O+}$: completely dissociated in water) at its first deprotonation, but is a weak acid ($\mathrm{p}K_\mathrm{a}$ value over that of $\ce{H3O+}$) in its second one.

Does it also hold for 2-sulfopropanedioic acid too, being a strong acid at its first deprotonation and being weak acids at its second to fourth deprotonations?


texts: Calculation of Atomic weight percentage in AAS

texts:
I am currently doing doping studies in a system similar to this ($\ce{A_{x}B_{1-x}}$) and I have to find atomic weight percentage of $\ce{B}$ element using atomic absorption spectroscopy(AAS). I have prepared different PPM of solutions according to the weight percentage of $\ce{B}$ element.

Example to prepare 10 atomic weight percentage of $\ce{B}$ in $5~\mathrm{ppm}$ solution, I have used this equation to calculate molecular weight:
$$\text{Actual mol weight}=\text{mol.wt}(A)\cdot x + \text{mol.wt}(B) \cdot (1-x).$$

In this case $x = 0.9$ and $1-x = 0.1$.

From this, I have prepared $5~\mathrm{ppm}$ of a solution of the doped material assuming that $10\%$ of $\ce{B}$ is doped completely (but in reality only very low percentage is doped).

I got the below data from AAS:

B (At wt %) Conc of sol(ppm)    AAS Conc(µg/ml)
    10          5                 1.5
    20          5                 0.9

From the above data, I have to calculate actual atomic weight percentage of $\ce{B}$.
My colleague has suggested this method in order to find $\text{Actual atomic weight percentage}$

$$\text{act.At.Wt.%} =\frac{\text{Obs.AAS.Conc(µg/ml)}}{\text{Sol.Conc(ppm)}}\cdot \text{At.Wt.percentage.of.}\ce{B}$$

Using this I got the results below.

B (At wt %) Conc of sol(ppm)    AAS Conc(µg/ml)   Actual B (At wt %)
10                5                  1.25            2.5
20                5                  0.9             3.6

But I have doubt in this method as you can see in the table the observed AAS concentration for 10 and 20 At wt % $\ce{B}$ is 1.25 and 0.9 (µg/ml) respectively. You can see that the AAS concentration of 20 At.wt % is lower than 10 A.wt %. But when we calculate actual $\ce{B}$ At.wt.% we can see that the 10 A.wt %  is lower comparing 20 A.wt %. Can you tell me whether the equation suggested by my colleague is correct or not? If not can you suggest any other method in order to find the actual atomic weight percentage?


texts: Complexity in computing the integrals involving higher angular momentum

texts:
I am quite familiar with Hartree Fock theory. However, writing it into program is an entirely different task, and that is where I have a couple of questions.

I wrote a Hartree-Fock routine in Python a couple of years ago. It involved a ultra-minimal basis: only one gaussian for two hydrogen atoms each. Kinetic energy term was pretty simple, so were the one-electron terms. Coulomb and exchange integrals were tricky, which involved evaluation of an erf. Now, my question is, if I included higher angular momentum basis functions (p,d,f,g type functions), what happens? Is it difficult to evaluate the J (Coulomb) and K (exchange) integrals because of the mathematical complexity? Or something else? Can someone give the math behind this and explain why it is difficult to evaluate?


texts: Hydrolysis of salts containing amphiprotic anion

texts:
I am trying to understand the derivation of pH of salt containing amphiprotic anions, but I am facing some difficulty:

Ionisation:

$\ce{HCO3^- + H2O <=> CO3^2- + H3O+};\quad K_\mathrm{a_2} $

Hydrolysis:

$\displaystyle\ce{HCO3- + H2O <=> H2CO3 +OH-};\quad \frac{K_\mathrm{w}}{K_\mathrm{a_1}}$

Taking the assumption: $\text{Degree of ionisation} = \text{degree of hydrolysis}$, or, $[\ce{CO3^2-}]=[\ce{H2CO3}]$, an approximate calculation of pH can be done by the relation:
$$\mathrm{pH}(\ce{HCO3-})=\frac{\mathrm{p}K_\mathrm{a_1}+\mathrm{p}K_\mathrm{a_2}}{2}$$

I don't understand the assumption $[\ce{CO3^2-}]=[\ce{H2CO3}]$. We know that $[\ce{CO3^2-}]=[\ce{H3O+}]$ and $[\ce{OH-}]=[\ce{H2CO3}]$. But if $[\ce{CO3^2-}]=[\ce{H2CO3}]$ then $[\ce{H3O+}]=[\ce{OH-}]$. Hence pH should be 7. I don't know where my logic is going wrong and it would be great if someone could help me clarify the derivation.


texts:
$\ce{Te(OH)6}$ has an octahedral geometry with $6$ $\ce{-OH}$ groups.

Is it a protonic acid (like $\ce{HCl}$) or a Lewis acid [like $\ce{B(OH)3}$]?

What makes $\ce{Te(OH)6}$ dibasic?


texts: Electrolysis of water for demonstration: ideal electrolyte for safety, stability, conductivity, and ease of maintenance

texts:
I'm developing a system for educational purposes where electrolysis of water takes place. The aim is to practically show how electrical energy can be converted to mechanical, by electrolyzing water, igniting the mixture of $\ce{H2}$ and $\ce{O2}$ produced, and accelerating a mass upwards.

Currently I'm using citric acid in distilled water ($4\%$ in weight, $18~\mathrm L$ water), platinum-coated mesh electrodes, $500~\mathrm W$ max power supply ($0\!-\!65~\mathrm{V_{DC}}$, $0\!-\!10~\mathrm A$). I'm wondering if there's any better option that meets the following requirements:

Not harmful to maintainers (that have to prepare and replace the liquid) and bystanders
Stable (not producing precipitates, and in general that can minimize the need for replacing the liquid)
Low/no interaction with the materials in the tank (Plexiglas, brass, platinum, silicone tubes, ABS)
Maximizes conductivity (the current setup at $20~^\circ \mathrm C$ has a conductance of $250\!-\!300~\mathrm{mS}$)
Not suitable for microorganism development (in the current setup algae develops in about two weeks)

If the last point can't be improved with just the electrolyte, I'd kindly ask for a suggestion for an additive that is not going to spoil the points above.


texts: Electrical and Thermal conductivity of electrum alloys

texts:
I have tried to search for this to little effect - I am trying to find electrical and thermal conductivity values for Electrum (a gold and silver alloy). Most sites mention the values depend on the percentage of gold and silver in the alloy, but provide no actual figures.

Is there a table out there that shows approximate electrical and thermal conductivity for electrum under different amounts of component metals in the alloy?


texts: What is the point group of hexachloridotitanate(III)?

texts: I found the answer to this question to be $D_\mathrm{3h}$ but I am not convinced. Can someone explain me with a diagram if possible and explain why it doesn't belong to the octahedral point group $O_\mathrm{h}$?


texts: Need 28% acetic acid from 98% glacial acetic acid

texts:
i need to make a solution of a 28% acetic acid, what i get is 98% glacial acetic acid. If someone could please guide me to make this solution.

I want to know the safety precautions i need to take when using 98% glacial acetic acid.

Also i would like to know safety precautions i need to take when using 28% glacial acetic acid.

Can i store it in PP narrow mouth bottles

How long will this solution stay good and also how to store it.

Thanks for your help.


texts: What is the product of the reaction of 2-methyl-5-phenyl-2-pentene with sulfuric acid?

texts:
The reaction is 2-methyl-5-phenyl-2-pentene with $\ce{H2SO4 }$

I have tried multiple attempts at this question but am still getting it wrong. I have no idea why any of these answers are wrong.

I know that the chain off the aromatic ring is weak aromatic activator and an ortho-para director. I figured para would be better than ortho because of the size of the chain but obviously both answers were incorrect. I then figured that $\ce{H2SO4}$ is just a strong acid so its basically $\ce{H3O+}$ but adding $\ce{H}$ and $\ce{OH}$ across the double bond in the chain did not work either.


texts: Change in enthalpy and entropy for the formation of nickel tetracarbonyl

texts:
I was working on an enthalpy/entropy problem and I had a question on predicting the signs of some reactions. For the reaction

$$\ce{Ni (s) + 4 CO (g) -> Ni(CO)4 (g)}$$

my textbooks says that when we predict the sign change in enthalpy and entropy, enthalpy is > 0 and entropy < 0. I'm not sure why this is since bonds are forming in this reaction and energy is being released (negative sign in enthalpy) and when a solid and gas react to form gas, it increases disorder (positive sign in entropy).

Am I understanding something wrong? Why is enthalpy > 0 and entropy < 0?


texts: Do weak acid/weak base neutralisation reactions go to completion?

texts:
I'm wondering if reactions that involve a weak acid and a weak base go to completion. For example, say we have equal amounts and equal volumes of acetic acid and ammonia being mixed together. Would this neutralisation reaction go to completion or would it reach a state of equilibrium?

$\ce{NH_3 + CH_3COOH <=> NH_4^+ + CH_3COO^-}$

Instinctively, I'm thinking that the reaction would be an equilibrium, since proton transfer should be able to occur between the products ($\ce{NH_4^+ + CH_3COO^-}$) to reform the reactants. Can anyone clarify if this is true?


texts: How is the reaction between Aluminium and Mercury Chloride possible?

texts:
Aluminium is coated with a thin layer of Aluminium Oxide. Why then do we write the reaction as

  $$\ce{2Al + 3HgCl2 → 2AlCl3 + 3Hg}$$

Shouldn't we first write an equation showing how $\ce{HgCl2}$ reacts with $\ce{Al2O3}$ ?


texts: How do I calculate the molecular mass of a complex in a complexometric titration with EDTA?

texts:
I had to titrate 0.35 mmol (3.2 g) of $\ce{Co2F2(Hdmpz)6(BF4)2}$ in a solution with 10 drops of 37 % $\ce{HCl}$, 10 mL of 4 M $\ce{NaOAc}$, 25 mL water and xylenol orange as indicator with  a 0.05 M EDTA solution.

Now I'm supposed to calculate the percentage $\ce{Co^2+}$ and then calculate the molecular weight of the whole complex.

Let's just say I saw color change at 16 mL EDTA. How do I calculate the percentage and the molecular weight? I'm also not sure about the molar ration $\ce{Co^2+}$:$\ce{EDTA}$.

If I just count the atoms it should be about 906 g/mol.


texts:
Is there a reason for why most medicines are in salt form?
Why not have them in conjugate base form?


texts: What exactly is the 'shuttle effect' in sulfur batteries?

texts:
Ref :

https://www.electropages.com/blog/2020/01/why-lithium-sulphur-batteries-are-taking-so-long-be-used-commercially

  Because they continually shuttle between the electrodes, they never change back into a neutral state (which the surface polysulphide ions do)

I don't think this explains the 'shuttle effect' clearly. I still don't understand what it is.

During discharging, lithium ions and sulfur form Li2S8 at the cathode, then it becomes Li2S4, Li2S2, Li2S with continued discharging. During charging, the Li2S move towards the cathode, now, why can't it be reversely reduced to Li2S4, Li2S8. Why can't they ever change back into a neutral state?


texts:
In the following question;

Apparently, an SN2 reaction ensues, where the iodine atom's supposed to cleave off with the less sterically hindered alkyl branch from both the oxygens. This is the solution:

That's what happens with the lower oxygen, but what's going on with the top one? In the second step, why doesn't the methyl attached to it cleave off with the iodine atom?


texts: Why are H+ and OH- ions preferentially discharged in the electrolysis of NaCl(aq)?

texts:
There are 4 types of ions in an $\ce{NaCl(aq)}$ solution: $\ce{H+}$, $\ce{OH-}$, $\ce{Na+}$ and $\ce{Cl-}$. According to the E.C.S. table, $\ce{H+}$ and $\ce{OH-}$ should preferentially discharge at cathode and anode, respectively.

However, according to the Wikipedia page on self-ionization of water, water only dissociates slightly into $\ce{H+}$ and $\ce{OH-}$ in neutral solution. (This is the reason why pure water conducts electricity poorly). Therefore, in the $\ce{NaCl(aq)}$ solution, the concentrations of $\ce{H+}$ and $\ce{OH-}$ ions are extremely small, and by comparison those of $\ce{Na+}$ and $\ce{Cl-}$ are much higher. As a result, it seems to me that $\ce{Na+}$ and $\ce{Cl-}$ should be preferentially discharged because of the concentration effect.

However, my chemistry textbook says that in fact $\ce{H+}$ and $\ce{OH-}$ are preferentially discharged, and hence the main products of the electrolysis are hydrogen and oxygen. So apparently my understanding is wrong. But where?


texts: How are $\sigma$ and $\sigma^\pm$ determined in Hammett plots?

texts: The Hammett plot is commonly invoked in organic chemistry to reason about the plausibility (or implausibility) of various reaction mechanisms. The vertical axis is essentially the logarithm of an equilibrium constant (or rate constant) measured relative to a hydrogen functional group, which I understand. However, I am at a complete loss for understanding what is being plotted on the horizontal axis, which conventionally are denoted $\sigma$ and $\sigma^\pm$. What are these parameters and how are their values determined for various functional groups? In practice it seems that people look them up in tables, but where do the values in these tables come from?


texts: How to calculate hydrogen from SMILES string?

texts:
How to calculate the number of hydrogen atoms from SMILES string?

For example,

SMILES String: C1=CC(=C(C=C1C(CN)O)O)O

The known result is C8H11NO3


texts:
I noticed that every time I put chocolate in the freezer, then I touch it or eat it, it somehow doesn't feel cold at all.

I figured that it must be that it heats up extraordinarily fast from body heat, because if it had a super high coefficient of heat then it would be just as hard to warm it up as it would appear to get cold.

What property would give chocolate that capacity? I've never seen any other substance be put in a freezer and somehow not feel cold.


texts: For calcium, the electron configuration is $\mathrm{1s^2\:2s^2\:2p^6\:3s^2\:3p^6\:4s^2}$. Does it mean there's no electron in d sub-shell? Also, how would one write the electron configuration for a calcium ion?


texts: Is it possible to speed up radioactive decay?

texts:
I’m aware that elements like $\ce{^14C}$ have a known half-life, which means that over a span of roughly $5730$ years, half of the $\ce{^14C}$ atoms decay into $\ce{^14N}$.

Are there any substances known to speed up this process, that applying it to $\ce{^14C}$ will catalyze a chemical reaction resulting in $\ce{^14N}$, or sticking them in a particle accelerator and slamming them together will result in $\ce{^14N}$, or otherwise transmute elements?


texts: Why can't one make C60 with a combination of hexagons and heptagons?

texts: $\ce{C60}$ has a pentagon-hexagon system. Why can't one make it from a hexagon-heptagon system, or a pentagon-heptagon system for that matter?


texts: Do polymerized cooking oils release free radicals

texts: I am seasoning a carbon steel wok and from what I understand it basically involves heating cooking oil on it until it gets to the smoke point and then forms a polymerized layer that makes it like a non stick pan.  I have also heard that as oil gets heated close to and past the smoke point it breaks down releasing free radicals and other unhealthy compounds.  My question is that when the heated oil polymerizes do these compounds get permanently locked up in the polymer or will they eventually get into the food cooked in the pan?


texts:
So I have need of performing a titration upon a fruit juice to determine acid concentration. I will be using 1M NaOH as my base. Seeing as the solution will be coloured, it would be difficult to use an indicator such as phenolpthalein. Thus, I would like to use a pH probe.

My Question:

While titrating, should I be aiming to reach a pH of 7 or should I be aiming to reach the ionic product constant of water (Kw) at the temperature that I am performing the titration at? (e.g.6.63 at 50 degreees celsius)

Thank you in advance for your time and knowledge.


texts: Why macromolecule ligands such as Crown ethers form more stable complexes than open chain ligands?

texts: This was in J. Huheey's book and no explanation was given


texts: The quantum mechanics behind periodicity of elements

texts:
Especially in high school/first-year undergraduate chemistry courses, we learn with great dedication the periodicities along groups and periods. There are various useful and interesting trends.
I wanted, however, to find the theoretical framework behind it which explains the trends through mathematical analyses. I skimmed through the book Physical Chemistry by Peter Atkins, but couldn't find much information.
So I was also considering the possibility that the trends were mainly discovered and investigated through experiments, and quantum mechanics was there only to provide some rough theoretical yet non-quantitative interpretations. (For example, explaining the fact that the $4s$ orbital has a lower energy level than $3p$ orbital using what's called the penetration effect, which says that there is a comparably significant value of $|\psi|^2$ for $4s$ than $3p$ for smaller radius despite the probability densities at higher radius or expectation values of radius)
Is there any qualitative analysis of such periodic trends using quantum theory? If so, where may I find it?


texts: What happens if a polymer's length is equal to its persistence length?

texts:
So, I've been looking into polymer chemistry to model breaking polymers for a biological model, and I've been a bit stumped by the concept of persistence length.

I know that if a polymer is significantly longer than its persistence length, it needs to be treated as though the ends are completely independent of each other thanks to thermal fluctuations bending it all over (the analogy I have is treating the polymer like a piece of cooked spaghetti). If I model a polymer like this, I need to use the words "3 dimensional random walk" to describe its shape mathematically.

I also know that if a polymer is significantly shorter than its persistence length, it can be treated like a rigid rod that might be a bit bendy, like a steel rod. This is significantly easier to model: I can just treat it as a line/arc that moves through space as a single particle.

But what happens if a polymer's length is about equal to its persistence length? How can the polymer be modeled then? What precisely does it mean for the polymer's movement?

EDIT: I've been debating the merits of just treating it like a flexible rod (like the significantly shorter than persistence length example) and calling it good just because of model simplification. If I do that, how off would I be from reality?

EDIT2: I've been doing further research and found something called a "worm like chain" model. I'm pretty fuzzy on what it means for the fiber, and I'm having trouble grasping how the fiber would move from an intuitive perspective; the visual for how I'd need to treat it isn't working, and the visual would help immensely with the actual modeling for the rest of the equations I need.


texts: Why can higher voltages lead to less efficient electroplating?

texts:
I was reading up on electroplating and I came across some things which really confused me:

Faraday's First Law says that the amount of metal plated onto the cathode is proportionate to the current, so it should be that a higher current= more metal plated onto the cathode (I assume).
And from Ohm's Law, a higher current= higher voltage so (by syllogistic reasoning) a higher voltage should give you more metal plated onto the cathode.

However this isn't the case, because I did an experiment recently where the highest voltage didn't produce the highest amount of metal plated onto the cathode. I did some reading on why, and I read (on the internet) that it's because when you increase the current by a lot, the ions formed at the anode can't keep up with the rate of electron flow and electrons just end up combining with other things in solution and no metal forms.

I have some issues with this though; I used a solution with ions already in it, so shouldn't there be no problem for me? Even if the ions cannot be formed at the anode fast enough, I have ions already in solution, so I thought it would be fine. Plus, the experiment was run for only 25 minutes, so I doubt they would've all been used up or anything.

Also, even if it were true that the current was just too high for the ions to keep up; wouldn't the amount of metal formed be at least equal to or greater than the amount formed for lower voltages? It's just that you're forming more metal in less time, ie it gets faster (I think); so you should get the same amount at say 5 V that you do that 3 V, even if towards the end of the experiment in 5 V it gets inefficient and you stop plating. Because the amount of ions or anything doesn't change.

Sorry for the huge amount of writing, I just thought it'd be easier if I explained my thought process. I'd appreciate it a lot if anyone could help me! Thanks so much. :)


texts:
I'm not positive what this questions is asking.  The prompt says "Write balanced equations for the following processes.  Chemical species should be the dominant ones at the given $\mathrm{pH}$. Show your work in deriving these equations."  Then the actual question is:

  Precipitation of aragonite ($\ce{CaCO3}$;  $K_\mathrm{sp} = 4.8 \times 10^{-9}$), at $\mathrm{pH}~8$.

The balanced equation would just be $\ce{CaCO3 -> Ca^{2+} + CO3^{2-}}$ .

I know that in an acid-base reaction I can use the $\mathrm{pH}$ as the $K_\mathrm{sa}$ to find the concentrations of the reactants and products, but I'm not sure where the $\ce{H+}$ would come in here.  I'm also not sure what finding the concentrations has to do with writing a balanced equation.  Does $\ce{Ca(OH)2}$ have something to do with this?

I could change the equation to $\ce{CaCO3 -> Ca(OH)2 + CO3^{2-}}$  and then calculate the concentrations, but is that what this question is even asking?  Thanks!


texts: Which elements have no liquid form at atmospheric pressure?

texts:
Carbon has no liquid form at atmospheric pressure. Is this unique amongst naturally occurring elements?

The more interesting and vague question is, is this property somehow important or related to the many other amazing properties carbon has on Earth or just a coincidence?


texts: Why, among different metals, only zinc is favourable for the dehalogenation of vicinal dihalides?


texts:
Imagine an arrangement of atomic orbitals in an alternate universe, in which the s subshell contains 2 orbitals instead of 1, and the p subshell contains 4 orbitals rather than 3. In which groups would you expect the anomalously low electron affinities to occur?

My thoughts are groups 3 and 7, due to the fact that they are "one away" from filling up their subshell. The groups would look like:

s: _ _ _ _  ... p: _ _ _ _ _ _ _ _

However, the answer says 4 and 8. Is there something I'm missing?

Edit: in terms of electron configuration blanks, it would be
s: _ _ ... p: _ _ _ _


texts: If hydrogen bonding in water was weaker, what happens to H+ ion concentration?

texts:
Water ionization becomes much less evident if the hydrogen bonds are just a few percent stronger but pure water contains considerably more $\ce{H+}$ ions if they are few percent weaker.

I found this line in some article. You can even copy/paste this line on search bar of Google. I didn't understood the latter part of this statement which is "but pure water contains considerably more $\ce{H+}$ ions if they are few percent weaker". The author is indicating to which of the following three situations?

only $\ce{H+}$ ion concentration will increase
both $\ce{H+}$ and $\ce{OH-}$ will increase
$\ce{H+}$ will increase and $\ce{OH-}$ will decrease that is the equilibrium constant remains same.


texts: Why do catalysts have limited turnover numbers in practice?

texts:
I quote the Wikipedia page definition for Turnover number:

  In other chemical fields, such as organometallic catalysis, turnover number (abbreviated TON) has a different meaning: the number of moles of substrate that a mole of catalyst can convert before becoming inactivated. An ideal catalyst would have an infinite turnover number in this sense, because it wouldn't ever be consumed, but in actual practice one often sees turnover numbers which go from 100 up to 40 million for catalase.

I'm trying to find reasons for why catalysts don't function infinitely in practice. My only thoughts are that maybe they eventually degrade from slowly reacting with other species they are exposed to, but then wouldn't this depend on the environment it is in rather than how much substrate it catalyses? I also assume that all product is taken away as it is produced.


texts: Calculation of the enthalpy change of reactions

texts:
First, I’m a high school student and I wonder why every textbook just tells you how to set up those equations and cancel them to get the entropy change but never tells you why you can cancel the same species on both sides.

Second, for example,

$\ce{2B + 3H2O -> B2H6 + 3/2O2} \tag{  $\Delta H= 762~\mathrm{kJ}$}$

$\ce{H2 + 1/2O2 -> H2O} \tag{  $\Delta H=-286~\mathrm{kJ}$}$

Here the textbook tells us we should add up two reactions in order to get what we want (I didn’t post the whole question, just go with this)

Now, why do we have to add the two whole reactions up instead of just change the $\ce{H2O}$ on the left side into $\ce{H2 + 1/2O2}$?  What I understand about this $\ce{H2 + 1/2 O2 ->H2O}$ is if we reverse it, we can say if $\ce{H2O}$ takes in $286~\mathrm{kJ}$ of energy, it will turn into $\ce{H2}$ and $\ce{1/2 O2}$. So why we can’t just add $286~\mathrm{kJ}$ to the equation? Why we still need to add the whole thing $\ce{H2 + 1/2 O2 -> H2O}$ to the other equation?


texts: Does there exist any data repository of chemical compound that gives the structure of the compounds with the help of coordinate geometry. It would be like each atom has a coordinate and the list of bonds it has with other atoms so that the 3D structure of the compound can be created from this very theoretical description?


texts: Correlation between functional group and viscosity of an organic compound?

texts:
I'm looking to explore the correlation between the type of functional group on an organic molecule and the viscosity of the compound. I know that viscosity is affected by intermolecular forces (Ion-induced dipoles, Ion-dipole, Hydrogen bonding, van der Waals), and that the type of forces present depends on the functional group. I'm aiming to explore viscosities of compounds with the following groups:

Alkenyl
Alkynyl
Hydroxyl
Ether
Aldehyde
Carbonyl
Carboxyl
Amide
Amine
Nitrile
Phenyl

How do the (absolute) viscosities of compounds with each of these groups (assuming single-functional group compounds) differ, and why (in terms of intermolecular forces present)? Are there any databases with values for viscosities that I could use?

Thank you for the help.


texts: How does the rate constant change with the change of the temperature?

texts:
In class, we discussed the following multiple-choice question.

The rate expression for a reaction is:
$$rate = k[X][Y]$$
Which statement is correct?
A. As the temperature increases, the rate constant decreases.
B. The rate constant increases with increased temperature, but eventually reaches a constant value.
C. As the temperature increases, the rate constant increases.
D. The rate constant is not affected by a change in temperature.

Considering the Arrhenius equation given below, the rate constant is dependent on the absolute temperature of the reactants and activation energy of the reaction.
$$k = Ae^{-\frac{E_\mathrm{A}}{RT}}$$
Taking the following limit as the absolute temperature approaches infinity reveals that the rate constant converges to the Arrhenius constant at very high temperatures. This is also evident when graphing the Arrhenius equation. Therefore, we conclude that option B is correct.
$$\lim_{T \to \infty} Ae^{-\frac{E_\mathrm{A}}{RT}} = A\lim_{T \to \infty} e^{-\frac{E_\mathrm{A}}{RT}} = A$$
However, when checking the mark-scheme, option C is listed as the correct answer. Is there a mistake in my reasoning?


texts: Rotation energy barrier for carboxypyrazolate

texts:
In this molecule, which is 3,5-dimethyl-4-carboxypyrazolate (unless I got it wrong):

I do not think there is free rotation around the bond indicated in red, because one can write a resonance structure with significant reasonable weight where a double bond would be located between the two groups.

However, how can I go further than that and qualitatively describe the energy barrier for the rotation. I have found (here and there) that in the case of benzoates, the barrier is in the range 3–6 kcal/mol. Should I expect it to be higher or lower in the above molecule?


texts: [3+1]-Cycloadditions of Sulfur Ylides and 1,3-Dipoles(?)

texts:
My question is basically regarding the stereoselectivity of the situation.

I am not being able to decide on the positioning of the sulfur ylide with proper justification.

In the attached hand-drawn image, I have considered the (1'-oxoalkyl) group away from the alkyl group $\alpha$ to the carbonyl. The other possible orientation is to direct in on the same side as the alkyl group,  but coming out of the page.

Each positioning leads to a different outcome, which is why I drew the final product with a "wiggly" bond.

Furthermore, the transition state that I have drawn really seems sketchy, and I feel I need some guidance on that part.

[3 + 1]- and [3 + 2]-Cycloadditions of Azaoxyallyl Cations and Sulfur Ylides


texts: Primitive Technology - Production of NaOH

texts:
We need to produce NaOH with primitive Technology. This is Part 1 of my Gilligan's Island Challenge series (Part 2). You are stuck on an island with access to a beach, a forest, a river, a lake, and a surface vein of coal.

I realize it can be made from $\ce{NaHCO3 + Ca(OH)2}$, and a person in a primitive technology scenario would be able to make some soda ash, but is there another way? $\ce{NaHCO3}$ might be tough to acquire in substantial quantities without access to a trona mine.

Would adding $\ce{NaCl}$ to a highly basic solution of, say, lime cause $\ce{NaOH}$ to form? If so, could it be extracted? Assume electricity is hard to come by.


texts: When does ratiometric measurement account for signal variations?

texts:
I've been reading about pH and ion sensors that rely on a ratiometric approach, which supposedly circumvents many problems of intensity-based methods such as dye bleaching, dye leaching, and fluctuations in source intensity. I can think of situations though when this might not be the case.

For example, fura-2 is excited at two independent wavelengths, and the two emissions are detected sequentially. If the excitation source intensity at either wavelength were to fluctuate, the ratio of the emissions would be off from the calibration. Another example would be a FRET sensor in which the acceptor dye leaches at a faster rate than the donor dye; the emission ratio of acceptor to donor would no longer match the calibration.

So when does ratiometric measurement account for signal variations like dye bleaching, dye leaching, and fluctuations in source intensity? Is it only when there is one dye and one excitation source? Am I missing any other requisites? It seems like if there's only a single dye that bleaches/leaches or a single excitation source that fluctuates, the change in dye fluorescence would remain proportional such that the emission ratio remains the same.

Thank you!


texts: Diamond filtering - is it real or bogus?

texts:
I always hear that some big corporations use "diamond dust" to filter water seven times to make "diamond clear" vodka. I tried googling something about using diamonds for filtering, but I could not find anything except corporate sites that tell us only the best things about "diamond dust filtration technology".

Is this just a bogus claim? Because I can not think about diamonds as a viable filtering material.


texts: Convert kinetic rate constant into a rate?

texts:
Can anyone tell me how I can convert a rate constant derived from first order kinetics (units are $\mathrm{h^{-1}}$) into an actual rate (turnovers/h)?

The scenario is that I know my rate constant for a molecule degrading in solution and it is $0.012\ \mathrm{h^{-1}}$. I know that I have $10^{14}$ catalyst molecules in the solution. How can I translate that into a number of molecules converted  per catalyst per hour?


texts: Why upon melting of PEO between crossed polars colours appear?

texts:
Crystalline PEO when under crossed polars shows distinct Maltese cross pattern. Being birefringent, when polymer crystal align with the polarizer or analyser it shows extinction regions (effect known as zero amplitude extinction). And as PEO crystallize in spherulites, it does lead to Maltese cross pattern. (As parallel and perpendicular crystal fibrilis lead to extinction). Because the fibrilis twist upon radial growth it also leads to banded extinction regions, known as zero birefringence extinction.

Upon melting, first the crystal fibrilis realign themselves enhancing contrast of crystalline spherulite, and then I can observe some of the colours appearing in the banded structure, that I haven't seen before. Why does it happen?


texts: Gaussian Error: Zero Point Energy Calculation on Fluoroform fails

texts:
I have been performing isodesmic reaction calculations and one of my molecules is Fluoroform. It has already been optimized and its frequencies checked at the HF level of theory. However, when I went to calculate the energy at  B3LYP/6‐311+G(3df,2p) I received an error. I have isolated my error to the route section.

Below is my input file:

#T B3LYP/6‐311+G(3df,2p) Temperature =0

Optimization of Fluoroform

0 1
C
F     1    B1
F     1    B2   2    A1
F     1    B3   2    A2   3    D1
H     1    B4   2    A3   3    D2

B1  1.490000000
B2  1.490000000
B3  1.490000000
B4  1.090000000
A1  109.4712206
A2  109.4712206
A3  109.4712206
D1 -120.0000000
D2  120.0000000

Additionally, here is the error output Gaussian prints on termination:

QPErr --- A syntax error was detected in the input line.
 #T B3LYP/6â€311+G(3df,2p) Temperature =
           '
 Last state= "GCL"
 TCursr=      3523 LCursr=        10
 Error termination via Lnk1e in /cluster/software/gaussian/gaussian-09-D.01/g09/l1.exe


texts: Why does olive oil make 90 degree grids on a nonstick pan?

texts: Whenever I add olive oil to my cold nonstick pan and try to swirl it, it ends up making these 90-degree grids. Is this something to do with the oil, the pan, or the interaction between the two? I find the regular spacing between lines rather interesting.


texts: Right conductivity of protein sample for Protein A purification of human IgG?

texts:
A sample from a cell culture has some IgG and this is to be purified using protein A chromatography. Based on the chromatography handbook from GE-Healthcare/Cytiva, the protein sample should have "physiological" pH and conductivities. This corresponds to a pH between 6-8, but it is not clear what the conductivity sould be. Is there a ballpark value for this?
Also in general, the series of buffers for Protein A chromatography including a wash step looks something like this

Binding buffer (physiological conditions) to equilibrate the column
Protein sample to load the column
Binding buffer (same as above) to wash impurities while retaining the protein
Elution buffer to unload the column

Does the protein sample have to have the same pH and conductivity as the binding buffer? If so, it has to be adjusted after coming from a bioreactor. What happens if the solution from the bioreactor already has a very high conductivity above that of the binding buffer?


texts: describing in words a primitive heated water vapor lift

texts:
The primitive lift illustrated in the left hand side of the following figure operates using heated water vapor ("gas") that pushes on a sealed piston. During its operation, the vapor undergoes the rectangular cyclic process shown in the right hand side of the figure.
I'm trying to describe in words how one might realize each of the four steps.
My idea is : We assume the system is isolated entirely from its surroundings such that it obeys the ideal gas law. First, heat is added through an external source to the gas while the piston is held fixed such that Temperature increases while the volume remains constant, therefore the pressure increases from $p_{1} \to p_{2}$ (A). Then, the piston is released and the gas is no longer heated. The volume will increase from $V_{1} \to V_{2}$ and the pressure will remain constant. When the piston reaches the top it is stopped and held still.
Here I'm blocked, I don't know how to explain a situation in which pressure decreases while volume is held constant .
Any help would be appreciated.


texts:
The dissociation of formic acid ($\ce{HCOOH}$) is:
$$
\ce{HCOOH -> H+ + COOH-}
$$

Why is there a charge on $\ce{COOH^{-1}}$
 though?  Is it achieved through:
$$1\times(\ce{C^{4+}}) + 2\times(\ce{O^{2-}}) + 1\times(\ce{H-})?$$

Does carbon exist as a 4+ ion?

Also, as a somewhat unrelated question, can an acid donate multiple $\ce{H+}$ ions (or can a base receive multiple $\ce{H+}$ ions)?

Thanks in advance!


texts: How to find maximum and minimum oxidation number of an element

texts:
I've researched around and some sources claim, that in order to find the minimum and maximum oxidation number you do this:

Maximum: the group the element

Minimum: the group of the element - 8

However I cannot get this to work for Fe? I'd appreciate a clarification. :)
It seems to work for Sulphur and what I've read about it's oxidations.

Maximum: 6
Minimum: 6 - 8 = -2

Don't metals always have a positive oxidation number?
Does this mean for Fe (iron) it's 0 to +3?

(I know this is a duplicate, sorry, however the others weren't answered and asked years ago).


texts:
What should be the oxidation state of $\ce{F}$ in $\ce{HOF}$.

As fluorine is the most electronegative element in the periodic table, it should be $-1$. But when I googled it, I found that many sources say it is $+1$ based on the fact that it is an oxidising agent.

Is there any theoretical way in which we can predict its oxidation no. or at least explain this anomaly.


texts: Chemical Kinetics - change to system conditions

texts:
This is a question from a very old AP Chem exam (2006) prep book which I am amusing myself with in my spare time which is kind of humbling. There is something I am missing with this question, one of several similar questions in the kinetics section.

Given the following reaction (which doesn't establish an equilibrium) :
$\ce{A (g) + B (g) -> C (g)}$
which of the following would increase the concentration of $\ce{A}$?

addition of $\ce{A}$ at constant $T$ and $V$
addition of $\ce{A}$ at constant $T$ and $P$
addition of $\ce{A}$ at constant $V$ and $P$

Now my first thoughts are to reason as follows :
If you add $\ce{A}$ and the volume is constant obviously the concentration of $\ce{A}$ increases. If you add $\ce{A}$ and keep $T$ and $P$ constant the $V$ will just expand and the concentration will be the same. But if I ignore the reaction this is a gas law / concentration question so it is out of place. But it isn't an equilibrium so none of that reasoning applies either.
Now if the reaction happens so slow it takes a year for $1\,\%$ of $\ce{A}$ to react I could just consider the reaction not even happening? If the reaction happens so fast that it is essentially over in 1 second then it seems like any change to A would be undone as fast as you could increase it. But it seems like I am missing something basic as there is nothing given regarding the rate.
There are several questions almost identical to this in the same section which just have other than $1:1$ coefficients in the equation.


texts: What is hybridisation of XeF6 in solid state?

texts:
According to the following formula:

Type of hybridisation/steric no. = (no. of sigma bonds + no. of lone pairs)

it should be $\ce{sp^3d^3}$, however according to my textbook it is $\ce{sp^3d^2}$ in solid state. That is how it was written(in my textbook), emphasising on the fact that "in solid state it is $\ce{sp^3d^2}$". How does solid state of a compound changes its hybridisation?


texts: Is it still possible for an amateur, a hobbyist, or a science buff to make relevant discoveries in chemistry today?

texts:
Consider astronomy. Hobbyists and amateurs are today still able to make small to moderate scientific contributions to their field. Is the same true in chemistry?

I think there might be at least two restricting factors:

The equipment needed to make scientific discoveries is far too expensive (e.g. hundreds of thousands of dollars/euros/whatever) for an amateur to obtain
Not having a bachelor's + master's degree (so being ready for a PhD) is too limiting ("too much to study alone").

If there is no "correct" answer for the field of chemistry in general, please post an answer per bigger sub-field (e.g. organic chemistry).


texts: What is the "resonance hybrid" of benzene?

texts:
In my book, to explain the structure of benzene, it referred to the idea of resonance:

  The idea of resonance is that the actual molecule is a definite structure that is a hybrid of two or more theoretical structures.

I partially understood this sentence, specifically how a molecule could have multiple structures, but am confused about what is meant by hybrid. Could someone please elaborate?


texts: How many hydrogen bonds can methanol make?

texts: I believe that it can form 2 hydrogen bonds, one with oxygen and the other with hydrogen but a classmate said that oxygen can form 2 hydrogen bonds? Is this true? I can't find anything on google to support or refute that claim.


texts: Mechanism for acylation of benzene with succinic anhydride

texts:
I've just started with EAS. I wanted to write down a mechanism for acylation of a cyclic anhydride (for some reason the formation of the carbocation is not given in my textbook). So I wish to know whether this mechanism is correct or now. Since this is my first attempt at writing one, I don't know whether it's correct.
The reaction:

What I came up with:


texts: Equilibrium constant for esterification process

texts:
Teacher told us that the concentration term for pure liquids and solids is always $1$. But online I found this reaction:

$$\ce{CH3COOH(l) + CH3CH2OH(l) <=> CH3COOCH2CH3(l) + H2O(l)}$$

According to this page on LibreTexts (search for "esterification" to quickly find it),

$$K_c = \frac{[\ce{CH3COOCH2CH3}][\ce{H2O}]}{[\ce{CH3COOH}][\ce{CH3CH2OH}]}$$

Shouldn't $K_c = 1$ as all reactants and products are liquids? The above expression even contains $[\ce{H2O}]$.


texts: Molarity vs Normality in labeling sulfuric acid

texts: Molarity (M) is defined as moles of solute per liter of solution while Normality (N) is defined as moles of reacting units per liter of solution.  Most texts use sulfuric acid as an example to demonstrate the difference: a 1 M solution of sulfuric acid is 2 N because each mole of sulfuric acid gives two moles of $\ce{H+}$ (the "reacting unit"). Why then is concentrated sulfuric acid labeled as 18 N when it should be 18 M and 36 N (according to my text's example above)?


texts:
How to tell the difference between octane-1-ol and oct-1-ene? The things I can do are:

check their solubility in water
use bromine water
use $\ce{KMnO4}$
use sulfuric acid

I assumed that checking the solubility would be a good idea because of the presence of an alcohol but will I notice a difference since the alcohol has 8 carbon atoms. And they all react with bromine water, $\ce{KMnO4}$ and $\ce{H2SO4}$. I think I'm missing something.


texts:
I know that FCC shows ABC type but I am confused about it. For simple cubic and body centered, it is pretty easy to work out the packing arrangement but FCC is giving me a headache.

What is this Wikipedia article trying to tell in the diagram and how did choose A, B and C? What's up with the different orientations?

Can somebody tell me these in a simple way as I can't solve FCC problems based on structure.


texts: If a solution is super-saturated is it possible to add a substance to it without allowing it to crystallise? Does a change in temperature have to happen and reduce it's saturation if I want to add another substance?


texts: Will a crystal of iodine lower the yield of an Grignard Reaction

texts:
I discussed the following today:

If adding an iodine crystal to a Grignard to make the reaction go. will this tiny crystal force some of the metal or reagent to be used
up. ergo, therefore, there is a lower yield (I know it is microscopic
change, this is not the question)

It is more about if it takes some of the metal and uses it up, maybe forming Mg-Iodide, so it cannot be used in the Grignard reaction, and I am not sure if Mg-Iodide cannot be used or if it actually catalyzes the reaction.
It is in the first step of forming phenyl-Magnesium bromide (or other reagent of the same type) reagent for use in step 2 of Grignard. I write bromide on purpose, so you can see that it is another halide than iodide.
Could it be the iodine catalyzes the reaction, or actually, some of the phenylmagnesium bromide is turned to phenyl magnesium iodide, which can also be used in the reaction? Ergo there is no loss in yield at all?
Imagine for step 1, forming only the Grignard reagent, I used iodine equivalents to 10% of, for example, of bromobenzene, and used Mg (not in excess), but the exact amount of Mg equal to bromobenzene, as 1:1 ratio, and the reaction normally went to 100% yield (it does not) but imagine it. Would I lose 10% from the iodine crystals?

can you tell me what the iodine crystals forms in the reaction and will it able to be used in the reaction or not?
will it catalyze the reaction instead?

Will you show me, with drawings, the intermediates or products of the iodine crystal?
Will it interfere with the yield, as it takes some of the magnesium and forms most likely $\ce{Mg-I}$ that is not used in the reaction, or is it I am asking you? It doesn't give any hints regarding lowering of yield. Will it help catalyze or form Grignard reagent with iodide? Why?
A pointer to what I am actually asking is. what happens to the iodine that is not used to remove hydroxide or etch the surface then what comes out of that will it continually as catalytic etch give $\ce{Mg-I}$ then Grignard reagent with bromide and back or what happens with it? will it use op the Mg turnings lowering yield.


texts: Why do we assume 100% ionization for acetic acid (a weak acid)?

texts: This is about a titration. The base titrant used is sodium hydroxide.


texts: Why can't electrons be transferred using hydrogen ions?

texts:
Recognizing how oxidation and reduction occurs is essential for analyzing and understanding biochemical reactions. Which of the following methods would NOT be employed in transferring electrons in biochemical reactions?
a) As hydrogen ions (correct)
b) Through direct combination with oxygen
c) Directly as electrons
d)As hydride ions

My problem is that, it doesn't say why hydrogen ions cannot transfer electrons, also I'm not sure what "hydrogen ions" exactly mean. What if you have a hydrogen ion with 2 or 3 electrons? Why can't that be used to transfer electrons?


texts: What are metal zip tags and belt buckles made of?

texts:
Metal zipper tags and belt buckles melt very easily and can be melted by heating it in the stove for 5 minutes. But other metals like aluminium refuse to melt even after hours.

If you leave it overnight, it dissolves pretty well in vinegar. I am sure they are made of metal, as I've melted it and cast some metal cookies. The metal is denser than aluminium, shiny when molten and cast, but surface tarnishes after 1-2 hours. I'm guessing it is some type of a zinc alloy.

The metal of the zip tag has the following characterisitics:

silvery
tarnishes into a dark gray
does not colour a flame in odd colours (like red , crimson , green etc.)
malleable (easy to bend a 5 mm thick square just by using leverage of hands and a surface to press down on)
brittle if bent a couple of times.
melts in a few minutes

So, what alloy or metal are they made of?


texts: Why bridged bicyclic compound isn't a preferred product over fused bicylic compound in Robinson Annulation reaction?

texts:
Why a doubly-fused cyclohexanone is formed instead of bridged cyclohexanone like product which would be more flexible (entropically-favoured)?

Also, the OH group not being at the bridgehead carbon unlike former compound, shouldn't it have a better chance of forming stable alkenone after dehydration as the preferred product formed in Robinson annulation?  The following image elaborates my doubt.

 (source : https://en.wikipedia.org/wiki/Baldwin%27s_rules#Rules_for_enolates)

As per the Baldwin rule for enolate, the enol-endo reaction and enol-exo reaction is favoured for both exo-tet and exo-trig for six/seven-membered chain (from the excerpt is provided as above image).

Both the alternatives follow six-membered exo-trig which is favoured according to above Baldwin rule. (Refer to the image where the carbon chain of both the alternatives is numbered.)
The bridged-bicycle compound has 3 faces, where each face has a 6-membered ring when it was visualized through ChemDraw 3D.
So, it seems both the alternatives as the product of Robinson annulation is favoured according to modified Baldwin rules.


texts: Major form of methyl 3-hydroxy pent-2-enoate?

texts:
I came across this question in a test:

  The enol form is the ________ form for 3-hydroxy pent-2-enoate?  (major/minor)

My argument is that the enol form must be more stable because of hydrogen bonding in the enol form and subsequent six membered ring formation (chelation). However the keto form has no such stabilization factor. Hence according to me the enol form must be more stable. But sadly, that is the wrong answer. What's going wrong?

Structure for reference:


texts: Measuring a high Michaelis constant using fluorescence

texts:
We have the task of measuring kinetic parameters of an oxidase reaction that has a $K_M$ of about $2 \,\text{mM}$. For that, we want to use a fluorescence assay based on Amplex Red. The latter is a fluorogenic substance of an upper detection limit of $5 \, \mu \text{M}$. At higher concentrations, the inner filter effect causes non-linear behaviour.

Usually, we would use substrate and fluorophore concentrations of a similar range of the $K_M$ value. Obviously, we cannot do that here, as the fluorophore concentration would be way above the upper detection limit. This led us to the idea of reducing the substrate, fluorophore, and enzyme concentration by the same factor to do measurements in a micromolar range. Later we could simply scale up the results.

We doubt that this method is possible as the Michaelis-Menthen kinetics never look at the ratio between substrates and enzyme, but only regard absolute substrate concentrations.

So our question is if the proposed method is in fact not applicable and if so, what your suggestions would be?


texts: Hybridization and excitation of electrons, how is it possible?

texts: When studying the structures of molecules by hybridization why we take into consideration of excitation of electron if the excited electron only stays in the upper shell by absorbing for only 10^-8 seconds{approximately }?


texts: Ionization Energies + Photooelectron spectroscopy

texts:
The problem that I am trying to solve is pasted as below.

For part (a) I identify the element to be Sulfur as they are 5 peaks which correspond to 1s 2s 2p 3s and 3p, The y axis values correspond to the number of electrons so X's configuration, as a result, is 1s^2 2s^2 2p^6 3s^2 3p^4
For part (b) 3s^2 and 3p^4 are the valence shells for sulfur. So the AVEE would be = (2x2) + (4x1.2)/ 6 which turns out to be 1.47 MJ/mol.
The real problem that I am facing is on part C.
For part (c) I have written that the element lies below X as down a group the number of energy levels(n) increases and the distance is greater b/w the nucleus and the highest energy electron. Moreover, the shielding effect down the group results in an IE1 decrease, so the attraction is weaker and the electron gets removed easily.
When I look back and read my answer to C I can see a clear mistake and that is that I am assuming that I know the IE1 value for X. Which I technically don't because in my Question it hasn't been stated. So my question is that how do I go about solving part (c). What approach should I be taking?


texts: How to calculate the number of prochiral carbon atoms in a complex organic molecule?

texts:
Calculate the number of prochiral carbon in the following compound.

The Wikipedia page on prochirality states:

  In stereochemistry, prochiral molecules are those that can be
  converted from achiral to chiral in a single step. An achiral species
  which can be converted to a chiral in two steps is called
  proprochiral.

My approach:

I first considered the sulfur atom to be prochiral as it satisfies the above condition, but it was pointed out, that this is incorrect as the S atom is already chiral.

My doubt:

But should even the double bond containing $\ce{sp^2}$ carbon atoms be considered prochiral?

According to what Martin postend in the comments I conclude that ("all" carbon atoms-4) in the compound are prochiral. I subtracted 4 chiral carbon atoms in the compounds. Tell me if there is still any mistake!
However, I am feeling that a carbon containing two hydrogen cannot be considered prochiral. The Wikipedia article states

  If two identical substituents are attached to a sp3-hybridized atom, the descriptors pro-R and pro-S are used to distinguish between the two.

But H atoms are not considered substituents in organic chemistry, see substituent .


texts: Why the reduction potential of the reaction AgCl (aq) /Ag + Cl- is +0.22V

texts:
The point is $\ce{AgCl_{(aq)}}$ is the same as $\ce{Ag+}$ + $\ce{Cl-}$ (again, in water)
So my reduction reaction would be
$$\ce{Ag+ + Cl- + e- -> Ag + Cl-}$$ then the equation is simplified by removing $\ce{Cl-}$ from both sides (Spectator Ion).

Now there is $\ce{Ag+ + e- -> Ag}$ which has a potential of 0.80V, so why the original equation is 0.22V.

PS: I know it takes more energy to break the bonds and thus Ag is more stable with Cl and less likely to reduce. But the subscribed (aq) doesn't mean the bonds have already been broken by water?


texts: Sublimation of Iodine from Iodine Povidone

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Iodine povidone is a complex of iodine and the polymer povidone. I am wondering if one were to heat it enough, the iodine would sublimate and could be collected. Normally iodine boils at 184.3 °C, according to wikipedia.

A video of how the procedure might work, except iodine crystals would replaced with boiled down iodine povidone: Sublimation of Iodine Time lapse

This can be used to purify iodine, so from my understanding, you would be able to vaporize the iodine and leave the polymer behind.

Does the complex with povidone change how this would work?

I apologize if my question is ignorant, as I do not have a great understanding of how complexes work.


texts: Reason for shorter bond between sulphur and oxygen?

texts:
I recently came across this sentence in my textbook:

  the bonds between sulphur and oxygen in oxides of sulphur ($\ce{SO2}$ and $\ce{SO3}$) are much shorter than might be expected for a single bond.

I feel it could be due to partial double bond character due to resonance.

And the same textbook gives another explanation:

  In these molecules, in addition to normal π bond, a π bond is also
  formed by the sidewise overlap of a filled 2p orbital of oxygen with a
  vacant 3d orbital on the sulphur). This is called pπ - dπ bond and
  results in bringing the two atoms closer and thus accounts for shorter
  bond length of $\ce{S-O}$ bond.

The reason provided in the textbook (as mentioned above) is definitely untrue and incorrect

Because of reasons mentioned in these posts

Why is the bond order in the SO₃ molecule 1.33 and not 2?
.
Hybridization of sulfur in sulfur dioxide

Please provide a explaination for the same (the title question).


texts: How does calcium chloride act as a sequestrant (food science)?

texts:
This Wikipedia page lists common sequestrants (with respect to food science). As stated on the page:

  A sequestrant forms chelate complexes with polyvalent metal ions, especially copper, iron and nickel, which can prevent the oxidation of the fats in the food.

To me, this behavior makes sense for every example listed except calcium chloride. I can certainly see chloride complexing these metal ions, but even then, I typically don't expect the chloride ion to reduce catalytic capabilities much.

I assume the calcium cation has an effect on these processes somehow, too. Otherwise, I would expect regular table salt to have the same effect, but, while discouraging bacterial growth, I don't think sodium chloride reduces the rate of oxidative rancidification.

Could it be as simple as the desiccant effect of calcium chloride keeping the polyvalent metal ions from dissolving? It would seem like a massive amount of calcium chloride would be needed to have the desired effect if that was the preservation mechanism involved.


texts: Is it true that Enthalpy can not be defined?

texts:
My teacher told us that only the ""Change in Enthalpy "" is definable.
 Whereever I looked for it, I got only an "equivalent " type definition like:  It's a thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume. But change in enthalpy also holds the same kind of definition.
Thanks


texts: What is the CNC bond angle in methyl isocyanate?

texts:
Methyl isocyanate, $\ce{HC3NCO}$, is a toxic liquid which is used in the manufacture of some pesticides. What is the approximate angle between the bonds formed by the nitrogen atom in a molecule of methyl isocyanate?
(A) $104^\circ$ (B) $109^\circ$ (C) $120^\circ$ (D) $180^\circ$

I answered (A), but the correct answer is (C) according to the marking scheme.
I thought it was a bent-shaped, because  the lone pair of $\ce{e-}$ would repel the bond pairs of electron (similarly to $\ce{H2O}$ or $\ce{SO2}$).
My current assumption is that the $\ce{e-}$ in $\ce{N}$ in $\ce{CH3NCO}$ forms $\mathrm{sp^2}$ hybridization (and therefore should forms a shape like ethene).
I'm not sure if my thinking is correct, so hopefully you can help me understand why (C) is correct and why (A) is impossible.


texts:
Say you had copper(II) sulfate pentahydrate as a solid.

In an aqueous solution, is it still referred to by its hydrated form? Is it still called copper(II) sulfate pentahydrate (aqueous) or simply copper (II) sulfate (aqueous)?

I guess what I'm asking here is does the "hydrate" label apply exclusively to solids?