texts: distillation of aqueous CAN solution for the purpose of a reversible and strong endothermic reaction in cool packs

texts:
I know calcium ammonium nitrate (CAN) is used for cold packs. By bending a small metal plate the salt gets dissolved in water (separated pack) and this process is endothermic.

I would like to heat this calcium ammonium nitrate solution to get back anhydrous CAN. Is there a way I can do it without safety issues?

Source 1 advices to heat it up to 210 °C.
Source 2 mentions the possibility to decompose at 60 °C into nitrogen oxides

Do you think I can heat the mixture up to 100 °C?


texts: Conformations of cyclohexane and flipping

texts:
Conformations of Cyclohexane doesn't answers my question

This is what Organic Chemistry by David R. Klein states:

  Notice that the chlorine atom is on a wedge, which means that it is coming out of the page: it is
  UP. The methyl group is on a dash, which means that it is below the ring, or DOWN. The two
  chair conformations for this compound are as follows:

  Notice that the chlorine atom is above the ring (UP) in both chair conformations, and the
  methyl group is below the ring (DOWN) in both chair conformations. The confguration (i.e.,
  UP or DOWN) does not change during a ring ﬂip. It is true that the chlorine is axial in one
  conformation and equatorial in the other conformation, but a ring ﬂip does not change confguration. The chlorine atom must be UP in both chair conformations. Similarly, the methyl
  group must be DOWN in both chair conformations.

I am having a confusion in the last paragraph. Why should the Chlorine be up even after the ring flip? Moreover, why are we even discussing if it is above the ring or not, as it has already come in the equatorial position?


texts: Mechanism of ring formation of an epoxide under acidic aqueous conditions

texts:
I am trying to figure out the mechanism of this reaction:

I think the $\ce{H+}$ will first attack the oxygen of the epoxide and another $\ce{OH-}$ will be added to the most substituted carbocation, which is the secondary carbon of the epoxide. This will form a glycol, but don't know where to go from there.

What is the mechanism that leads to that product?


texts: Precipitation of AgCl from the tap water solution of the group 2 chloride

texts:
I had this question about an experiment where the group 2 chloride was dissolved in distilled water and excess $\ce{AgNO3}$ was added to the solution to form $\ce{AgCl}$ precipitate. One of the sub-questions read

  State how the amount of $\ce{AgCl}$ will change if tap water is used to dissolve the group 2 chloride instead of distilled water (will the amount of $\ce{AgCl}$ formed increase or decrease) and explain why.

Can someone please explain how the amount of $\ce{AgCl}$ formed will change if tap water is used? I assumed that tap water is chlorinated and so the amount of $\ce{AgCl}$ formed will increase. I don't know if this is right.


texts: Mathematically balancing chemical equation yields weird results

texts:
I found this equation while testing my equation balancer:
$$
\ce{a C7H6O3 + b C4H6O3 -> c C9H8O4 + d C2H4O2}
$$

Obviously, $a = b = c = d = 1$ is a solution. However, if we were to bring in some maths:

$
\begin{cases}
7 a + 4b &= 9c + 2d\\
6a + 6b &= 8c + 4d\\
3a + 3b &= 4c + 2d\\
\end{cases}\\
\begin{cases}
a &= \frac{11}{9}\alpha - \frac{2}{9}\beta\\
b &= \frac{1}{9}\alpha + \frac{8}{9}\beta\\
c &= \alpha\\
d &= \beta\\
\end{cases}
$

This leaves us with many ways of balancing the equation:

when $\alpha = 1, \beta = 1$, $a = b = c = d = 1$; $\ce{C7H6O3 + C4H6O3 -> C9H8O4 + C2H4O2}$
when $\alpha = 1, \beta = 2$, $\begin{cases}
a &= 7\\
b &= 17\\
c &= 9\\
d &= 18\\
\end{cases}$; $\ce{7 C7H6O3 + 17 C4H6O3 -> 9 C9H8O4 + 18 C2H4O2}$
when $\alpha = 2, \beta = 1$...

From what I know, this happens when the equation consists of 2 or more independent equations (as is the case here: More than one way of balancing a chemical equation). However, here the two equations are:

$$
\ce{11 C7H6O3 + C4H6O3 -> 9 C9H8O4}
\\
\ce{-2 C7H6O3 + 8 C4H6O3 -> 9 C2H4O2}
$$

What is concerning here is that the second equation has a negative stoichiometric coefficient. My question is, is a negative coefficient acceptable in an equation, and in this case which is the correct way to balance the equation?


texts: How many lumens from 1 gram of flash powder

texts: Does somebody know how many lumens we get from lighting 1 gram of flash powder in pure oxygen (or normal) environment? I'm thinking about $\ce{KClO_4} $ (60%) + $\ce{Al}$ (40%)  flash powder and quite fast flaming due to lighting it up with electricity.


texts: Why does $\ce{-NHMe}$ show -I effect. I think it should be opposite. I know that $\ce{-Me}$ groups are electron donating in nature. So the nitrogen atom will have a small $\delta^-$ charge. So then why would it still be electron withdrawing?


texts: Characterisation of gold-silver alloy nanoparticle

texts:
I have various compositions of gold-silver alloy nanoparticles.
I would like to characterize my nanoparticles and confirm that they are alloys.
Aside from the qualitative analysis of the colour and using UV/vis to identify the number of plasmon bands, what other methods can I use to confirm the presence of alloys?


texts: I plan to do some amateur chemistry with some basic equipment. I've watched hours of youtube videos for how to bend and polish glass tubing and push it through rubber stoppers, and I've seen diagrams of such tubing attached to rubber or silicone tubing, but nothing showing how to do that. I've even searched through catalogs of equipment and seen lots of specialized gadgets with hose barbs and such, but nothing basic. I just want to do a simple thing: have a rubber stopper with a glass tube in it, and attach that directly to a flexible tube. Nothing fancy, just one tube connected to another. I see it in diagrams like http://www.mctcteach.org/chemistry/C2224/labman/vacfilt/filter7.htm , but it gives no explanation. What am I missing?


texts: Energy absorbed by a system in isothermic process in which the phase changes from liquid to gas

texts:
A system contains $x$ mole of material, with surface area $S$ is pressed by a mass $M_1$ (no fraction and no any other outer forces involves). Let $\Delta H_\mathrm{l\rightarrow g}$ be the transition enthalpy from liquid to gas. The system is position in $(T,P_1)$ such that the material phase is liquid for those temperature and pressure values ($T$ and $P_1$). Now instantaneously the mass $M_1$ is decreased to to an unknown value which we denote $M_2$ so the pressure decreases. In case that the temperature stays constant until the inner pressure is equal to the outer pressure $(T,P_2:=\frac{M_2g}{S})$ system gets to back to equilibrium, and the material phase in $(T,P_2)$ is gas, I wish to calculate how much energy was absorbed by the system till it gets to pressure equilibrium $(T,P_2)$.

In the question is says that the volume of the liquid can be neglected when compared to gas' volume. And that the volume of the water is independent of the pressure.

What I did so far:

The chemical equilibrium pressure (i.e the pressure in the phase transition point) can be calculated because the exercise gives the triple point $(T_\triangle , P_\triangle)$ so using the transition enthalpy constant and the constant $T$ of the process, one can calculate $(P_\mathrm{l\rightarrow g, eq},T)$ (using Clausius–Clapeyron relation). And by $PV=nRT$ one may calculate $V_\mathrm{eq} = \frac{nRT}{P}$ the volume in the chemical equilibrium point. By the unstruction $V_\mathrm{eq}$ is the total volume of the material (we neglect the liquid volume)

We know the starting inner pressure which is $\frac{M_1g}{S} \text{[Pa]} $ and by the given instruction the pressure doesn't change the liquid volume we learn that until the phase transition point, the volume of the system stays constant $V_\mathrm{eq}$ which we calculated above.

When the system gets to pressure equilibrium point $(T,P_2=\frac{M_2g}{S})$ we don't know the volume or $P_2$ because $P_2$ is unknown how every we not that its larger then $V_\mathrm{eq}$.

I'm pretty much stuck here, I don't see how to translate this information to evaluate the amount of energy absorbed. It seems to me that maybe one more piece of information is needed, but the exercise doesn't give one.


texts: Is Gibbs free energy the sole determiner for spontaneity?

texts:
If a reaction has negative $\Delta G$, can we then say with certainty that the reaction will be spontaneous?

Is negative $\Delta G$ the sole determinant for spontaneity?


texts: Can I equalise osmotic pressure using two different solutes?

texts:
I understand that there is a pressure gradient between an aqueous solution, e.g. salty water, and, say, pure water due to osmosis. My question is, is it possible to match or almost match, the osmotic pressure between two solutions of different solutes, but using a solution with a different solute. For example, would it be possible to make the osmotic pressure gradient between salty water and some other solution zero, assuming both are at the same temperature and pressure?

I am not a chemist, so purely qualitative answers are helpful.


texts: Feasibility of Electrophilic attack on the Nitrogen over the Phenyl ring of Aniline

texts:
I have learnt that the '-NH2' substituent attached to the phenyl ring, owing to the substitutent's highly positive mesomeric effect, activates the phenyl ring quite a lot for Electrophilic Aromatic Substitution, so much so that it easily forms a tri-substituted product when Br+ is used as an electrophile with Aniline, and that a protecting group such as Acetyl (introduced using Acetic Anhydride) has to be introduced on the Nitrogen to deactivate the ring for just monobromination to occur.

This made me wonder that if such is the influence of the '-NH2' on the benzene ring then why would the Nitrosonium ion generated in diazotization prefer attacking the lone pair of Nitrogen instead of the electronically enriched benzene ring on the ortho or para position?

Initially I lazily (and wrongly) attributed it to perhaps some stronger bonds forming between similar atoms, i.e Nitrogen-Nitrogen bonds being stronger than the Carbon-Nitrogen bonds.

But, more interestingly I realized that this line of reasoning wouldn't apply to my above stated acetylation of the Nitrogen in Aniline, for in that case too there isn't an Aromatic Substitution taking place and there are no Nitrogen-Nitrogen bonds.

In short, what is the reason for the feasibility of Diazotization and Acetylation in the way they occur with Aniline? Why aren't electrophilic aromatic substitution reactions taking place? I may have erred in my basics, please help me out.


texts: How will the periodic table change due to redefinition of the kilogram (May 2019)?

texts: The definition of a kilogram has recently been changed. What effect, if any, will this change have on data on the periodic table?


texts: Does solute concentration vary significantly with depth?

texts: If I dissolve glucose in an ordinary beaker filled with water, are the concentrations of glucose at the top and bottom significantly different? What if we use NaCl as the solute? Is there a molecule large enough to ``sink'' to the bottom, and if so would it still be classified as a solute? Likewise, are there solutes which are lighter than H2O, so they float upwards?


texts: dsp2 and sp3 hybrid orbital shapes in coordination chemistry

texts: Why is $\mathrm{dsp}^2$ square planar but $\mathrm{sp}^3$ tetrahedral in shape? I am unable to find a reason anywhere. I know how to figure which hybridisation a compound is, but not why.


texts:
In an exothermic reaction, the value of equilibrium constant increases with the rise of temperature because,

$\Delta H < 0$ ( exothermic reactions)

$\Delta G = \Delta H - T\Delta S$

Now if $\Delta H $ and $T\Delta S$ are negative and positive respectively, the overall value of $\Delta G$ is also negative. (For positive entropy)

$\Delta G = -RT\ln K$   (where $K$ is equilibrium constant)

Since $\Delta G$ is negative, the value of $RT\ln K$ becomes positive and as $\Delta G$ increases equilibrium constant increases.

Is this logic right?


texts: Polymer Slurry used in boring foundation holes?

texts: I watched a video on the construction of Burj Khalifa, Dubai. The construction engineers answered that they're using a special type of protection known as Cathodic protection to protect from the corrosion due to local ground water. They told a compound named "Polymer Slurry" (What's that?). They're using viscous Polymer Slurry as their basic coat to dump the high density & low permeability concrete in order to create a "GOOD FOUNDATION". What is it made of? (Simply any polymer?) And what does it do? Does it actually repel water? Many organic compounds repel water... Then Why this?


texts: Which cyclohexane conformation is more stable?

texts:
I got this question wrong on a test and I don't know why:

  Question: Which conformation is more stable?

  Answer: the chair on the left is more stable.

I thought that the ring conformation has zero ring strain so I'm confused.


texts:
Is this a valid mechanism? I think it is. It is just a simple acid base mechanism.

Could I increase yield though by using a stronger base than heavy water? Perhaps heavy sodium hydroxide? Or is chloroform sufficiently acidic?


texts: Why do they use graphite electrodes in the Hall–Héroult process?

texts:
In the Hall–Héroult process of extracting aluminium from aluminium oxide, the electrolyte is a liquid mixture of cryolite $(\ce{NaAlF6})$ and aluminium oxide $(\ce{Al2O3}).$ The cathodes and the anodes are made of graphite.
During the electrolysis process, aluminium is deposited at the cathode and oxygen is liberated at the anode. Some of this oxygen reacts with the carbon in the graphite to form carbon-dioxide, thus slowly burning away the anodes. Thus, the anodes have to replaced periodically.
But if this is the case, why do they use graphite anodes at all? Why don't they use anodes of some other, less reactive material? I'm pretty sure there are many out there that would fit the bill.


texts: Producing soap from sodium carbonate and oil

texts:
Can we get soap by mixing $\ce{Na2CO3}$ from seaweeds with oil?

I am not good at chemistry and saw this in the anime Dr. Stone. I just want to know if it is true or not.


texts: Can vicinal dihalide produce conjugated alkene in strong base?

texts:
In Klein's Organic Chemistry (3rd edition), p. 410, we learn that vicinal dihalide can produce alkyne in strong base. And on Reaxys I see many reactions of this sort. For example:

However, why isn't the conjugated alkene, which should be more stable, the major product under such conditions?

Somebody once gave me an explanation, to the effect of "the hydrogen geminal to the halide is more acidic, hence more easily eliminated." However, Smith's Organic Synthesis (4th edition), p. 121 says the following:

  [In the following reaction] $\mathrm{H_a}$ is more acidic than $\mathrm{H_b}$ since it is attached to the less substituted carbon. The base should react with
  the more acidic hydrogen atom, which would lead to the less substituted alkene, 3-ethylhex-1-ene, but that is not the major product.

This suggests that we cannot base our logic on the acidity of the hydrogen atoms.


texts:
I have bought some anhydride of trichloroacetic acid (TCA) and would like to prepare an acidic solution. My problem is, that I don't know how much "powder" to mix with how much water to produce an x% acidic solution of TCA.  I am aiming for as close to 100% as possible. From what I know, I need to measure pH to derive the concentration (I only have some litmus paper to do that)? Does there exist formulas or tables, that I can follow? Sources of these?

EDIT: Based on a comment, I obtained these values:

I have bought 1 kg of TCA powder of

1000 g / 163.38 gmol^-1 = 6.1207 mol
18.01528 gmol^-1 * 6.1207 mol = 110.27 g of water

somehow I need to dissolve 1 kg of powder into 110.27 mL of water. How can that work? I doubt 1 kg of powder can be dissolved in such a tiny amount of water.

EDIT2: Wikipedia says Solubility in water: Soluble in 0.1 parts. Does this mean I need 0.1 * TCA amount for a 100% solution? That would mean I need to dissolve 1 kg of TCA in 100 mL of water.

EDIT3: If you have any idea about the true solubility of TCA, please help,  there seems to be a lot of misinformation out there. 1000 g / 100 mL seems very strange to me! You can see the strange data here, from multiple sources.

EDIT4: I have asked my Chinese supplier about how they prepare their TCA solution and he said they use 120g - 154.1g / 100 mL recipe for a "standard" solution. The concentration can then be calculated by mole or by mass, but naturally is never 100%. The only way a 100% liquid TCA could exist would be to melt it down into liquid form.


texts: The influence of diffuse functions on electron density calculations

texts:
I am not a quantum chemist, but I am (starting to be) a user of electronic structure software. In the picture (screenshot) is the electron density of the same molecule. On the left I calculated the density using B3LYP/6-311++G*, on the right I used B3LYP/6-311G*.

I have visualized the densities using Avogadro. In Avogadro, I can visualize a few of the HOMO/LUMO orbitals. The screenshot is of the first LUMO for both calculations.

In the images, red indicates electron rich areas, blue indicates electron poor areas. The molecule (caffeine) was in the presence of point charges which created an electric field, explicitly polarizing the electron density.

My Question: Why does the presence of diffuse function (the plus's in 6-31++G*), make the LUMO orbital opposite in electron density? I understand allowing diffusion would change the electron density, but it looks nearly exactly opposite now (however the total density looks pretty much the same - see last image).

Note that these are screenshots of just two orbitals, the overall density plots shown below, look very similar.

I am not a quantum chemist, so please use small words...


texts: Why is atomic mass unit/unified atomic mass defined against Carbon 12?

texts:
I have searched the web all over this question and I have not really found an answer to my satisfaction. From my understanding of the topic so far, I understand that reason why concept of unified atomic mass works better than providing absolute mass of protons/neutrons (in grams or kilograms) is because "u" provides between clearer presentation of relative masses among elements in whole numbers than the negative exponents would in regards to absolute mass. If this premise is true than why not define atomic mass unit in terms of multiple of protons and neutron? Like since proton and neutron are roughly equal in mass ~ 1.66* 10^-24g. Why not say 1u = mass of one proton and 1 neutron. Why does the definition of amu need to include 1/12 of carbon 12, because mass of 1/12 of carbon gives me mass of 1 proton 1 neutrons and this seems redundant to me?
But now if we accept the definition of amu as 1/12 of carbon 12? Why not include other elements like amu is 1/1 of Hydrogen atom,  1/4 of helium atom, 1/16 of oxygen atom, because all this would would give me same value of 1u= 1.66*10^-24g ? If anyone can give their input on this, that would be grea.


texts:
I have a ligand $\ce{L}$ and a receptor $\ce{R}$. As can easily be shown, with dissociation constant $K_\mathrm{D} = \frac{[\ce{L}][\ce{R}]}{[\ce{LR}]}$ the fraction of receptors occupied by ligand is

$$\theta = \frac{[\ce{LR}]}{[\ce{LR}] + [\ce{R}]} = \frac{[\ce{L}]}{[\ce{L}] + K_\mathrm{D}}$$

It's easy to see that the fractional saturation of receptors is independent of receptor concentration. Now here's where I get confused. Let's say we have a constant volume of $\pu{1 L}$ with $\pu{5 mol}$ ligand and a $K_\mathrm{D}$ of 5:

$$L = 5, \quad K_\mathrm{D} = 5 \quad \to \quad \theta = 0.5$$

If we have $\pu{10 mol}$ of receptor total ($[\ce{LR}] + [\ce{R}] = 10$), then $\pu{5 mol}$ will be bound to ligand. Now let's say we increase the number of receptors by $10\times$. Our formula for $\theta$ is independent of $[\ce{R}]$ or $[\ce{LR}]$. We now have $\pu{50 mol}$ receptor bound to ligand.

That being said, we only had $\pu{5 mol}$ ligand to start with, which is itself a paradox. Can someone explain to me where I went wrong?


texts: Why doesn't carbon form  3 $\pi$ bonds? If s-s overlap is possible between 2 carbon atoms,then it will be possible for 3 p orbitals to overlap laterally .


texts:
Is it possible to chemically convert methane into propane?

If so, what is involved and is it economical?


texts: What determines a substance's energy of activation with air?

texts:
Ice will melt when heat is applied; paper will catch fire. In trying to figure out why — what the difference is between things that melt and things that catch — I found "Burn, Char, Melt" by Roberto Gregorius, who says it depends on

  whether the substance easily forms compounds with some oxidant [usually oxygen]. This term "easily" can be taken to mean that the energy required to start the reaction (called the energy of activation) is low enough so that the reaction starts (as in striking a match), or the compounds produced in the burning are low enough in energy that there is a tendency to form it. Of these two, energy of activation is usually the controlling factor in deciding if a reaction will take place.

All right, so what determines a substance's energy of activation with air? (Wikipedia isn't helping.) In case it isn't obvious, I'm uneducated in chemistry, and an answer tailored accordingly, to the extent possible, would be ideal.


texts: Converting Fischer formulas to Newman projections

texts:
How are line diagrams of molecules converted to their Newman projections? All I got from looking it up is that one may convert a Fischer formula to an eclipsed conformation directly, and that this may further be converted to other conformations.

Doesn't that stop the molecule from having a unique stereochemical configuration?


texts: How does a hydroboration mechanism actually work?

texts:
Let us say that you have 1-propene reacting with $\ce{BH3-THF}$ and then later with hydrogen peroxide and sodium hydroxide. I eventually get 1-propanol. The way it was explained to was that after reacting with $\ce{BH3-THF}$  we have $\ce{CH3CH2CH2BH2}$ and after the second set of reagents we get our product.

But, I never understood the mechanism, the explanation seems forced. $\ce{BH2}$  goes to the less hindered carbon which explains why its at the terminal. And then for some reason, $\ce{BH2}$  gets replaced by $\ce{OH}$.


texts: Reaction of concentrated nitric acid react with metallic lead?

texts:
Here is my work:

Concentrated $\ce{HNO3}$ should first decompose into $\ce{NO2}$, $\ce{H2O}$ and $\ce{[O]}$. Nascent oxygen should combine with $\ce{Pb}$ to form $\ce{PbO}$. Now $\ce{PbO}$ should neutralize acid to form $\ce{Pb(NO3)2}$.

Therefore, the net products would be lead nitrate, $\ce{NO2}$ and $\ce{H2O}$.

Is this right?


texts: Does an increase of area lead to more collisons in a confined jar of gas?

texts:
I'm reading a lecture by Richard Feynman in which he is talking about the behaviour of gas molecules/atoms within a confined vessel.

The confined vessel is a cylinder with a piston to stop the water molecules from flying out.

However this follow sentence has me stumped

"Clearly, the force is proportional to the area, for if we increase the area but keep the number of molecules per cubic centimeter the same, we increase the number of collisions with the piston in the same proportion as the area was increased."

If the area of the piston is increased, but number molecules remain the same, would there not be less force as the collisons are spread out?

I'm thinking of this in the same vain as shoes exerting less pressure than high-heels due to the increased area.


texts: Free energy change in collagen hydrolysis

texts:
In now-deleted comments on this answer, a user with a self-proclaimed chemical engineering background claimed that the reactions that take place when slow-cooking meat are endothermic and require far more energy than actually heating the meat. My intuition says this can't be - the meat would rapidly cool itself down if removed from the heat source, the sous vide circulator would have to work hard the whole time not just during initial heating, the bonds in the collagen are presumably not terribly strong, and, well, heating mostly-water things takes a lot of energy! But I don't want to assume too much.

I believe the primary interesting reaction here is collagen conversion, hydrolizing it into gelatin, and the collagen is something like a few percent of the meat by mass. (When cooking something like this, the rapid reactions have already taken place: the meat looks cooked, and it gets slowly more tender over time as the collagen breaks down.)

So, how much energy does that actually require?


texts: Ionic Radius of Iodine in High Temperature Form

texts: The ionic radius of iodine in the high temperature form can be determined once the unit cell is known, but how can I calculate the radius of $\ce{I}$ given that the cubic lattice parameter is 6.10 Å.


texts: Ammonium is a weak acid but isn't it considered a strong conjugate acid as a salt's ion?

texts: I'm learning about salt hydrolysis in school and this just jumped out at me. How can $\ce{NH_4^+}$ be both a weak acid and a strong conjugate acid? Since $\ce{NH_4^+}$ is a weak acid it has a strong conjugate base $\ce{NH_3}$. However, as part of a dissolved salt, since $\ce{NH_4OH}$ is a weak base, then $\ce{NH_4^+}$ is considered a "strong" conjugate acid. How can we reconcile these facts? Are the definitions slightly different for a salt ion and a normal acid?


texts: What makes an atom favor another one when bonding, and should there be enough atoms for both parts?

texts:
I'm learning chemistry through Khan Academy and I have 2 pretty basic questions.

Oxygen (O) has 6 electrons on it's last shell, so it needs 2 more to become stable. Hydrogen (H) has 1 electron, so it needs 1 more. O might combine with 2 H's, creating H2O, and it might combine with another O, creating O2. It can also create H2O2.

QUESTION 1: So, given a hypothetical solution (or environment, or whatever), with only O and H atoms, what will make O to favor a bond with another O instead of a bond with 2 H's (or vice-versa)? Both situations will make it stable.

QUESTION 2: Also, if we assume that, in that solution, there's a limited number of both O and H atoms, and after all bonds are made, there's only one O atom and one H atom left, will that H atom bond with the one O atom left, since that will make the H stable (albeit not the O atom), creating a HO molecule ? So, I guess what I'm asking is, will bonds only be made when there's enough atoms for both parts to become stable?

Thanks.


texts:
I am currently reading a paper titled "Polystyrene Nanoplastics-Enhanced Contaminant Transport: Role of Irreversible Adsorption in Glassy Polymeric Domain" (link here).

In the paper, the authors mention the term 'desorption hysteresis' as the mechanism of the interaction between nanoplastics and contaminants. Here's the relevant excerpt (from the introduction section):

    ... at low nanoparticle (i.e., “carrier”) concentrations significant facilitated
    transport of organic contaminants requires not only strong adsorption of contaminants to the carriers, but also significant desorption hysteresis (a collective term referring to both slow desorption kinetics and thermodynamically irreversible adsorption) of contaminants from the carriers. Desorption hysteresis can either be due to the physical entrapment of contaminants in the complex matrices of the carriers, or strong specific adsorptive interactions that lead to irreversible binding of contaminants to the carriers.

I am having some difficulty in understanding what do they mean by adsorption hysteresis. From what I've read, hysteresis is how the system in its current state is related to some past state, but I don't understand this concept fully.

Could someone please explain what is desorption hysteresis? I couldn't even understand the explanation in parentheses (right after the term in bold above). Is it about the rate of desorption of contaminants from nanoparticles?


texts: Destabilization of antibonding MO vs stabilization of bonding MO

texts:
My textbook writes that

  The net energy stabilization due to the occupation of a bonding MO is equal to the net energy destabilization due to the occupation of the corresponding antibonding MO.

Essentially, it claims that these two quantities are equal.

(Image source: SparkNotes)

Shouldn't the antibonding orbital be destabilized more than the bonding orbital is stabilized, though?


texts:
At least to me, the contents of chapters 5 & 6 given here are representative of discussions on chemical bonding given in nearly all intro general & organic chem books, the statements in those chapters are mainly memorization (to me anyway). I basically don't find it rigorous enough, leads to more rather than less confusion and doesn't give any in depth discussion (similar to the way the quantum mechanics sections of those books are rote assertion ignoring all of the math).

I'm in the middle of a physics-based quantum mechanics course, so I'm developing the conceptual & mathematical tools to read a serious explanation of lewis bonding, polar-covalent bonding etc... but my book doesn't mention much in detail on this topic either, and apparently not even Pauling's QM book mentions much on the topics.

I'm really hoping somebody would have a quick look at the contents of chapters 5 & 6 of the first link & offer a recommendation of a rigorous reference or four on the contents of those chapters - I really can't face the headache I'll get reading chapters like those again due to all the confusion they lead to by dumbing it down, I need something more rigorous if such a thing exists, thanks a lot :)


texts: How does an hybridised orbital become unhybridised after bond cleavage?

texts:
In $\ce{CH4}$, $1 s$ and $3 p$ orbitals are hybridised into four $sp^3$ orbitals. But on homolytic bond cleavage an unpaired electron remains in an unhybridised $p$ orbital?

Similarly in heterolytic bond cleavage of $\ce{CH4}$, the methyl carbocation has an unhybridised empty $p$ orbital?


texts: How can normalities be interchangeably used?

texts:
So I was doing the following question on stoichiometry . The part $\pu{1.80N}\ \ce{HCl}$ can also be written as $\pu{0.9 N}\ \ce{   H_2SO_4}$  but I don't understand why .

$\pu{10 g}$ sample of 'gas liquor' ($\ce{NH}^+_4$ salt) is boiled with $\ce{NaOH}$ and the resulting $\ce{NH3}$ is passed into $\pu{60 ml}$        of $\pu{1.8 N}\ \ce{HCl}$ . Excess $\ce{H_2SO4}$ required $\pu{10cm^3}$ of $\pu{0.40 N}\ \ce{NaOH}$. What is the % of $\ce{NH3}$ in gas liquor?

I got the answer but just can't understand why the two can be used interchangeably.


texts: Ok, so I learned about the equilibrium constant. Now, I've seen that the equilibrium constant of burning is extremely small $(K \ll 1)$. here, I have a question. you see, $K$ is still NOT 0, which means that the forward reactions happen at least a tiny bit. Then, shouldn't we see some parts of anything burning at least a little bit?


texts: How can one say pressure is constant in thermodynamics?

texts:
When a gas expands by  b charles law pressure increases
$$\frac{p}{t}=k$$
thermodynamics says:
$$dQ=dU+PdV$$
so herfe one is considering constant pressure but how b charles law says it changes?So shouldn't it be:
$$dQ=dU+PdV+VdP$$
can't we apply a variable external pressure?


texts: Comparing basicity of imidazole and 2-imidazoline

texts:
I recently sat for an exam in which I was asked to compare the basicity of the above compounds. I thought imidazole would be more basic because it is aromatic but according to the answer key 2-imidazoline is more basic. The reason provided is that the lone pair on imidazole is a part of aromatic system and hence it's not basic.

Shouldn't the other lone pair which is on nitrogen double-bonded to carbon be basic? After all it's not involved in resonance due to being out of plane of the pi-system. What is the real reason behind higher basicity of 2-imidazoline (if it is really more basic)?


texts: Multi-step organic synthesis using benzene

texts:
I have this project that I've been struggling with. I'm already given the reactant and product, so basically what I have to do is to figure out the steps needed to get the product.

I figured that some of the steps would include the Friedel-Crafts acylation and nitration, but after that, I'm not too sure what other steps I'd have to take. Any help will be very much appreciated!


texts: How does 1-bromo-2-fluorobenzene react with lithium amalgam?

texts: How does this organometallic reagent react with 1-bromo-2-fluorobenzene? Does it react like Grignard reagent? If the product of this reaction is then reacted with furan, what will be the final product? I can guess there will be a benzyne intermediate, but I am not sure.


texts: Calculate accelerating voltage required to separate two particles in a magnetic sector analyser

texts:
So, in mass spectrometry we have the following equation to describe a magnetic sector analyser,
$$\frac{m}{z}=\frac{B^2r^2e}{2V}.$$

Lets say that I have two particles with different mass/charge ratios,
$$\frac{m_1}{z_1} = 120.9,\quad \frac{m_2}{z_2} = 121.0,$$
and I have $B=2\text{T}$, $r=25\text{cm}$. For example, what accelerating voltage $V$ do I need to apply to separate these two particles? What criteria do I have to determine whether two particles are separated?

** ** EDIT ** **
I don't know where to start with this. So even though you don't generally answer homework-like questions on this forum, some pointers in the right direction would be greatly appreciated!


texts: Are Hartree-Fock solutions eigenfunctions of the electronic hamiltonian?

texts:
$\newcommand{\Ket}[1]{\left|#1\right>}$
$\newcommand{\Bra}[1]{\left<#1\right|}$

I'm currently revising for my qualifiers, and I've come across a point of confusion, one that several places give seemingly contradictory results.

To my understanding:

In Hartree-Fock, the variationally determined ground state, $\Ket\Phi$, is not an eigenfunction of the electronic hamiltonian. It's composed of eigenfunctions of the Fock operator. It's an approximation of the ground state of the Hamiltonian.

(1) Is this all correct so far?

(2) If so, is it justified to use it in numerical derivations as an eigenfunction of the Hamiltonian,
i.e. can we write $\hat{H}\Ket\Phi\overset{?}{=}E_{0}\Ket\Phi$ or are we restricted to $\Bra\Phi\hat{H}\Ket\Phi=E_{0}$


texts: LC-MS: Can a "bad" peak still be interpreted

texts:
I have done an untargeted metabolomics study using LC-MS. There is one peak that matches to a biologically relevant compound but analyte eluted at the beginning of the LC run and the peak shape is far from ideal.

Do I assume the peak is an artifact, or can I say that there is a compound with that m/z in my sample? Ideally I would run the experiment again with standards, but I cannot do that due to time constraints. Someone else will follow up on the interesting compounds that I've identified and I wouldn't want to send them in the wrong direction.

Below is the peak in question, and following it is an example of a "good" peak from the same dataset.


texts: Is a negative pH level physically possible?

texts:
A friend of mine was looking over the definition of pH, and wondering if it is possible to have a negative pH level. From the equation below, it certainly seems possible—just have a $1.1$ (or something $\gt 1$) molar solution of $\ce{H+}$ ions:
$$\text{pH} = -\log([\ce{H+}])$$
(Where $[\ce{X}]$ denotes the concentration of $\ce{X}$ in $\frac{\text{mol}}{\text{L}}$.)

If $[\ce{H+}] = 1.1\ \frac{\text{mol}}{\text{L}}$, then $\mathrm{pH} = -\log(1.1) \approx -0.095 $

So, it is theoretically possible to create a substance with a negative pH. But, is it physically possible (e.g. can we create a 1.1 molar acid in the lab that actually still behaves consistently with that equation)?


texts: Stereoselectivity of hydroboration of dihydrofuran

texts:
The above compound undergoes hydroboration. I originally thought that the $\ce{OH}$ group can attach to any of the 2 carbons plus there are 2 possible enantiomers at each position. So there should be 4 different products formed.

However the answer states that only below compound would be produced:

Why is this the only compound that is produced? Also if the $\ce{OH}$ group had to be attached to one of the carbons wouldn't it be more likely to attach to the carbon next to the oxygen since it will be more electrophilic?


texts: How to read a chromatography calibration curve?

texts: I am a high school student who has been studying a bit of chromatography. I came across calibration curve during class and I trying to figure how to read it and use it? I have no clue how to read off the graph nor do I really now the use of it. Can someone please explain what information I can extract from this graph and possibly provide an example if that's fine?


texts: Calculate the weight percent of limestone in a rock sample

texts:
A 1.245 g sample of limestone ($\ce{CaCO3}$) is pulverized and then treated with 30 mL of 0.035 M $\ce{HCl}$. The excess acid requires 11.56 mL of 1.010 M $\ce{NaOH}$ to be neutralized. Calculate the %wt of limestone in the rock.

The first balanced equation would be:

$$\ce{CaCO3 + 2HCl -> CaCl2 + H2O + CO2}$$

Then:

$$\ce{HCl + NaOH -> H2O + NaCl}$$

I figured out the moles of $\ce{CaCO3}$ if that's useful for this problem 1.245 g of $\ce{CaCO3}$ / 100.089 g (molar mass)= 0.0124 M

I have this but I don't know the next steps on how to solve the problem.


texts: In a reaction between Calcium Ammonium Nitrate or Urea with water, does Nitrogen Content and Purity affect how cold the solution gets?

texts:
Recently, I bought an ice pack that contained Calcium Ammonium Nitrate, and realized that it really didn't get cold. I came to the conclusion that perhaps Urea is more effective, yet it is still puzzling to me that in a perfectly secure ice pack, it got to refrigerator water temperature.

I was thinking, perhaps purity of compound and nitrogen content (46% in Urea vs ~23% in CAN) could make a difference.


texts: Why is acetone and diethyl ether miscible, but not water and diethyl ether?

texts: Acetone and Water are miscible, and water and diethyl ether are not. So why are acetone and diethyl ether miscible if water and acetone seem to have similar polarities?


texts:
In order to be a gas does the pressure exerted by the gas has to be more than the atmospheric pressure?
Really simple, I think yes to this question but teacher says no. So what is your view into this?


texts: Why don't alkynes undergo preferential anti bromination to the degree that alkenes do?

texts:
Alkenes, for the most part (unless there is a phenyl group or highly ionising solvent) undergo almost exclusively anti addition of bromine. However, under similar conditions alkynes, although undergo preferential anti-addition, it is not as exclusive as alkenes. Even with electron withdrawing substituents like two $\ce{COOH}$, only 70% is anti. (Peter Sykes, page 182)
Why?


texts:
Why does sulfuric acid displace more volatile acids from salts?
My textbook says that sulfuric acid can displace more volatile acids from metal salts.
How is $\ce{HCl}$, which is not even a reactant, 'displaced' from $\ce{NaCl}$, as there is no $\ce{HCl}$ to be displaced?


texts: Is there a blanket term for all variants (both nuclides and ions) of a chemical element?

texts: I'm hoping to catalogue the various nuclides and oxidation states of an element but can't find a single term that describes them all, save for "chemical element variations". Is there a specific term used for this?


texts: What are most common condition for reduction of hematite to magnetite?

texts: I found that hydrogen can reduce $\ce{Fe2O3}$ to $\ce{Fe3O4}$ under anaerobic conditions, but since I dont have $\ce{H2}$ in my lab what should I use to convert hematite into magnetite? and what conditions are used - temperature, pressure, partial pressure of oxygen and other important factors.


texts: Halogenation by Phosphorous tribromide vs using HBr

texts:
My textbook introduced PBr3 by stating that it leads to an inversion in stereochemistry since it always goes through an SN2 pathway, unlike using HBr.
My question is that since Br- is a reasonably good nucleophile, so I assume it would most likely proceed through SN2 in a substrate with a secondary carbon anyway. Both pathways seem to me to be extremely similar with the exact same attacking species eventually (Br-) and an excellent modified leaving group attached (H2O+ and OHPBr2).
What exactly is the difference and the advantage (other than being non-acidic) that make halogenation by PBr3 a better method?


texts: why do we obtain a sigmoid curve in vapour pressure versus temperature graph

texts:
i have recently got a question in an assignment, which was somewhat like this

  what would be the shape of curve obtained in a graph between vapour pressure & temperature of a binary solution in a closed vessel

generally we do all the experiments regarding vapour pressure in a closed vessel, so the volume must remain constant and from the formula $PV=nRT$, the number of moles remains constant in a binary solution, as volume is remaining constant we get the equation as $Y=mX$, which is a straight line passing through the origin,
but the answer was a sigmoid curve, how did we get that, can i get an elaborate answer for this quiery.


texts: Gromacs: What can be reason of getting final potential energy greater than the starting one?

texts:
I wanted to optimize potential energy of a molecule using Gromacs software (v. 5.0.4, single precision). I was really surprised when I discovered that after running Conjugate Gradients integrator, the final potential energy was greater than the starting one. Does anyone know what can be a reason of that?

Perhaps I don't understand what is optimized because potential energy went down and up during simulation.

Fragment of logs:

Step 0, Epot=4.840216e+06, Fnorm=2.899e+05, Fmax=4.849e+07 (atom 672)
....
Step 56, Epot=8.949906e+03, Fnorm=2.368e+03, Fmax=4.351e+05 (atom 783)
...
Step 244, Epot=8.550481e+07, Fnorm=2.406e+05, Fmax=4.658e+07 (atom 54660)

Energy minimization has stopped, but the forces have not converged to the
requested precision Fmax < 10 (which may not be possible for your system). It
stopped because the algorithm tried to make a new step whose size was too
small, or there was no change in the energy since last step. Either way, we
regard the minimization as converged to within the available machine
precision, given your starting configuration and EM parameters.

Polak-Ribiere Conjugate Gradients converged to machine precision in 244 steps,
but did not reach the requested Fmax < 10.
Potential Energy  =  8.5504808e+07
Maximum force     =  4.6581140e+07 on atom 54660
Norm of force     =  2.4062566e+05


texts: Deriving The Triple Point Temperature and Pressure as the following expression

texts:
Using the usual notations of $\Delta H_\text{fus}$, $\Delta H_\text{vap}$, $\Delta H_\text{sub}$, as well as ($T_\mathrm l,p_\mathrm l$) and ($T_\mathrm s,p_\mathrm s$), which corresponds to the temperature and vapor pressure of liquid and solid phase, I have to derive the triple point temperature and pressure.
My strategy is to use the Clausius-Clapeyron Relation:
$$\frac{\mathrm dp}{\mathrm dT}= \frac{\Delta S}{\Delta V}$$
but the rest is history...
Could someone help me with
$\Delta H_\text{fus}$ and ($T_\mathrm s,p_\mathrm s$)?
So that I know that I'm moving in the right direction?


texts: Explanation of Specific Chemical Shifts on an H-NMR Spectrum

texts:
Recently, I've been looking into chemical shifts on H-NMR Spectrums and I came across a graph I didn't quite understand...

As you can see from the spectrum attached, the signal emitted from the protons near the Cl (colour coded orange) is further downfield than the signal emitted by the protons near the O (colour coded dark blue). However, shouldn't the protons near the Oxygen be further downfield due to their proximity towards the more electronegative atom? How can this be explained?


texts: Comparison of basicity of o-phenanthroline and ammonia

texts:
I was trying to compare the basicity of o-phenanthroline and ammonia.
According to me, the factors that are seen in o-phenanthroline are:

o-Phenanthroline has two nitrogen atoms at the 1,10 positions.
It has a free lone pair on one nitrogen that is not delocalized due to resonance.
The nitrogens are $\mathrm{sp^2}$ hybridized which is more electronegative compared to the $\mathrm{sp^3}$ lone pair on ammonia.

However, would there be hydrogen bonding in its conjugate base? If so, then how do we compare its basicity with a base like ammonia?


texts: Does nitrogen deaeration need to be performed in a fume hood?

texts:
I have a couple electrochemical cells I will need to sparge (deaerate) with nitrogen prior to and possibly during my experiment (the solution is .1 M NaOH). Does this need to be done in a fume hood?

From what I've read, it seems that $\ce{N2}$ gas isn't a huge danger, but if you're in a confined space it can cause a severe lack of oxygen. If that is the case, would a normal-sized classroom count as a confined space? Also, from what I understand about deaeration, the nitrogen bubbles escape the solution with impurities, but also with oxygen, so maybe in my case the lack of oxygen wouldn't be a problem.

This may be a simple question, but it has been difficult for me to find standard procedures for sparging a liquid with an inert gas, and I want to make sure I'm taken all the necessary precautions and steps.


texts: Equation for reaction of tin and iodine to produce tin(IV) iodide

texts:
Tin(IV) iodide is prepared by direct combination of the elements.
Add 2.00 g of granulated tin to a solution of 6.35 g of iodine. Write an equation for this reaction.

Attempt:
1. Determine the amount of tin using moles = mass/molar mass. This yields a result of 0.017 mol $\ce{Sn}$.
2. Determine the amount of iodine using moles = mass/molar mass. This yields a result of 0.5 mol $\ce{I}$.
3. Determine the ratio of tin to iodine. Using relative amounts, for every 1 mol $\ce{Sn}$ there are 3 mol $\ce{I}$, so the ratio is 1:3. Because iodine is a diatomic molecule, I will adjust accordingly, so the ratio becomes 2 mol $\ce{Sn}$ to 3 mol $\ce{I2}$ or 2:6.
4. Construct the formula:
$$\ce{2Sn + 3I2 -> SnI4}$$
with excess tin and iodine.
Is my procedure correct?


texts: Doubts on Diffusion/ Effusion of gases at different pressures

texts:
Let's start with a question:

  "One mole of nitrogen gas at 0.8 atm takes 38 s to diffuse through a pinhole, whereas one mole of an unknown compound of Xenon with fluorine at 1.6 atm  takes 57 s to diffuse through the same hole. Calculate the molecular formula of the compound."

It is a question where pressures of the gases are not similar. Could be solved quite easily, if we calculate the rates of diffusion ($r_{N_2}$ and $r_{un}$) of each gas separately as no. of moles of the respective gas diffused per unit time, find the ratio of the rates and then equate this ratio, with another ratio found using pressures and molar masses of the given gases, i.e, with
$$\frac{r_{N_2}}{r_{un}}= \frac{p_1}{p_2}\sqrt{\frac{M_{un}}{M_{N_2}}}$$, ($M_{un}$ and $M_{N_2}$ are molar masses of the unknown gas and nitrogen gas respectively) and finally find the no. of fluorine atoms attached with xenon from the value of molar mass of the unknown gas.

It's fine that way. But we also know that, volumes of a gas diffused per unit time gives us rate of diffusion too. And in the question above, the volumes (in case they were given instead of moles) would have been different because of different pressures. Consequently, the first ratio (the ratio involving volume and time) would have been different compared to the ratio involving moles and time. And that would have affected the final value of molar mass and thus messed up our solution.
So my question is, what would be the actual cause of such a situation? And how to fare in those situations?


texts: Hybrid orbitals, photoionization and time dependence

texts:
Wikipedia, in the article on Orbital Hybridisation, states the following:

  One misconception concerning orbital hybridisation is that it incorrectly predicts the ultraviolet photoelectron spectra of many molecules. While this is true if Koopmans' theorem is applied to localised hybrids, quantum mechanics requires that the (in this case ionised) wavefunction obey the symmetry of the molecule which implies resonance in valence bond theory.

(Source; emphasis mine)

I am wondering about the bolded part. I interpret it as meaning that the wavefunction is an eigenfunction to both the Hamiltonian and to the symmetry operators of the molecule's point group. To me, the bolded part then seems equivalent to stating that the molecule emerges from the ionization process in one of the eigenstates of the ionized system, and I can understand how the symmetry requirement would hold true in that case.

However, my intuition wants to think about the ionization process in such a way that the departing electron leaves a "hole" somewhere in the wavefunction, which then evolves over time as a superposition state; i.e., the system does not emerge in an eigenstate, and the "hole" left in the wavefunction will "travel" through the molecule in some way. I am under the impression that the time-dependent wavefunction at any point in time could in principle break the symmetry imposed by the molecular point group.

So this leads me to two questions:

Am I wrong in thinking that superposition states do not necessarily have to obey the stated requirement about molecular symmetry? And
is my picture of a time-dependent molecular wavefunction immediately after ionization viable?

Update: I am of course aware of the argument that we can make unitary transformations of the overall wavefunction as we please, as it leaves the total electron density distribution and energy unchanged; this is also how hybrid orbitals are formed when starting from an MO picture. However, because the orbitals involved in hybridization belong to different energy eigenvalues, this creates a time-dependent superposition state with no defined energy. In extension, hybridization silently implies that the MO energies themselves are not observables that would describe the initial states in the ionization process. And, in addition, the hybrid orbitals do not necessarily form irreducible representations of the underlying molecular point group anymore, and do thus not obey the bolded symmetry requirement in the quote above.

So here are two questions which are quite closely related to the two I had originally formulated above:

What is the justification for the assumption that the MO energies are not observables? And
how is it justified from the perspective of the Wikipedia article that we have to obey the symmetry of the molecule in the ionized product state, but for the hybrid orbitals in the ground state, we can for some reason disobey the same principle? Isn't this highly inconsistent?


texts: Catalyst that combines oxygen and hydrogen

texts:
Are there any known catalysts that can combine hydrogen and oxygen into water?

Does this type of reaction have a name? Trying to search for information, it seems to be all about splitting hydrogen and oxygen, is there any work on combining these and some catalysts that could be used?


texts:
Arrange the following pyridine derivatives in the order of increasing stability
of adduct formed with $\ce{BBr3}.$ Explain briefly.

I'm pretty confused about which structure is the most stable. I'd say structure III is the most stable as it has two methyl groups to donate electrons to nitrogen and increase its Lewis basicity.
However, I think III may not be the most stable because of steric hindrance. In fact, structure II could be the most stable as the methyl group is closer to nitrogen and there's no steric hindrance. Therefore, the answer should be III < I < II.
Is my reasoning correct? Are there any factors to consider for stability?


texts:
Several companies are offering a service to turn ashes of human remains into diamonds.
Does anyone know any details about the chemical aspects of the process?

I have no idea, but suspect that the ashes are composed mostly of phosphates and oxides. Where does the carbon hide? Any carbonate would have decomposed at the creation temperature. Or does the cremation chamber has such a high $\ce{CO2}$ partial pressure that $\ce{CO2}$ from burners is captured by the $\ce{CaO}$?

How is the carbon then extracted?

Also, diamond is normally made out of graphite, which agrees with a statement on the LifeGem website.

Let's assume they can squeeze out a little $\ce{CO2}$ by heating the ashes in an oxygen stream. Then they concentrate the $\ce{CO2}$ on a molecular sieve, use the Sabatier reaction to create $\ce{CH4}$ which they decompose on a hot metal wire. Then they dissolve that in acid and get a little bit of powder rich in $sp^2$ bonds and similar to graphite. Could one make diamonds out of that?

On the other hand, the page mentioned above states that they first extract the carbon and then turn it into graphite. How do you turn a few mg of fine carbon powder into graphite?


texts: Using Arrhenius equation to calculate the ratio of two reaction rates

texts:
For two reactions,

  $$\begin{align}
\ce{A ->[$k_1$] B} \tag{1} \\
\ce{A ->[$k_2$] C} \tag{2}
\end{align}$$

  you have determined that the activation energies are $\pu{71.9 kJ/mol}$ for $(1)$ and $\pu{142.8 kJ/mol}$ for $(2)$. If the rate constants are equal at a temperature of $\pu{321 K}$, at what temperature will $k_1/k_2$ be equal to $2$?

I know I have to use the Arrhenius equation

$$k=A\exp\left(-\frac{E_\mathrm A}{RT}\right),$$

and I've tried solving for $T$ after filling in my data into the formula as ratios, ie $k_1/k_2$, $E_\mathrm{A}^{(1)}/E_\mathrm{A}^{(2)}$, etc, but I can't seem to get a coherent answer. Any guidance on figuring this out would be much appreciated.


texts: I use borax to clean everything. the other day I thought it would be a good idea to mix a little borax with my shampoo while showering.  After lathering it on my scalp about 30 seconds it began to give off a really bad chemical smell, almost like a perm solution. What was the borax reacting with the product in my hair or the shampoo?


texts: Comparing the boiling points of common organic molecules

texts:
The order I was provided with is(comparing molecules of similar molecular mass from each);
alkanes< ethers< esters< aldehydes< ketones<< alcohols<< carboxylic acids<< amides
Where << is supposed to signify a considerable hike.

Here, how do you compare esters and ethers?
I assume the higher position of the carbonyls with respect to those are due to the keto-enol tautomerism they have(with the enol forms  having hydrogen bonding).But how are ketones placed below alcohols?
Why are amides at the very top? Nitrogen being less electronegative than oxygen, I would've thought the hydrogen bonding in those wouldn't be as strong as in the carboxylic acids.


texts: Choosing LC-MS modifier - why only acids?

texts:
During method selection our chromatographists have options like NH4, TFA, Formic Acid. What's the point of choosing only between acid? Why not use the strongest that guarantees ionization? The sample contains small organic molecules.

And if the analyte is an acid, don't we want to have a base as a modifier? Otherwise how can we ionize it using ESI?


texts: Non-conducting substance with a glass transition temperature around 400 to 600 °C?

texts:
Am looking for a substance to seel two pieces of ceramic that will have molten plastics flowing between at 300+ °C however silver solder circuit traces inside the device prevent me from going much above 600 °C without destroying them – otherwise I would be using some form of pottery glaze but the lowest melting one I have found reference to is around 1000 °C.

The ideal would be something I could bring back up to the glass point and separate the pieces for servicing.

Can any one either suggest a compound or recommend a resource that would allow me to search based on constraints like I outlined?


texts: How to determine stable electron states in ionic and covalent bonds?

texts:
I'm working on a program that needs to determine if a bond between two or more elements will result in a stable state.  I understand at a high-level how to fill electron subshells using the Aufbau principle, but I also read that in some cases, electrons will jump from a lower energy shell or orbital to a higher one in order to maintain a stable state (Filling Electron Shells).

For example, if I want to determine if Hydrogen and Nitrogen will form a stable bond I would fill the shells for Nitrogen like so:

When adding Hydrogen, would the two electrons in the 2s shell jump to the 2p shell because with the one electron from Hydrogen the HN would then have a full 2p shell? Like this:

Or is this not a stable state? Would it require a large amount of energy to excite or promote those two 2s electrons to the 2p shell?

I'm trying to understand if there are rules or heuristics I can use to estimate if two ore more elements will bond (on there own w/o adding a large amount of energy to the system) using their valence electron configuration like this, or if there are too many exceptions, making it not a simple programming task to estimate this.


texts:
For the reaction below:

NH4+ + H2O -> NH3 + H30+

I have the following values from a table to use:

And in the solution manual they tell me to use the Ka for this reaction. Why is this? Why do we use the Ka for NH3 when it is NH4 acting as an acid?


texts: Which would have a more intense transition: a low spin d6 complex or a high spin d5 complex?

texts: I have an assignment question for second year inorganic which asks to rank the intensity of d-d transitions for a number of complexes. Two are $\ce{[Fe(OH2)6]^3+}$ and $\ce{[Fe(CN)6]^4-}.$ Both will have Laporte-forbidden transitions, but which will be 'more forbidden', so to speak?


texts: Nucleophilic Substitution Reaction of Alcohol

texts:
What is the final product?

According to me, it's option (3). But given answer in the booklet is (2).

Given primary alcohol undergoes SN2 reaction to produce isopentyl bromide and the latter again undergoes SN2 to form isopentyl cyanide.

Can someone please help?


texts: What Ion gets reduced in this aqueous electrolysis?

texts: In an electrolysis of tin(II) iodide ($\ce{SnI2}$) with led cathode and nickel anode, why is it that the tin ion gets reduced and not the nickel ion?


texts: Why do gases need to be cooled to liquefy/solidify?

texts:
My book states:

  Gases do not liquify on compression only, although molecules come close to each other and Weak forces operate at a maximum.

Why is it that we cannot just keep on compressing  gas till it solidified or liquified? Why do we need to reduce its temperature?
Also, if that is true, what would happen if I kept compressing a gas, without siphoning out the excess energy?


texts: It is possible to make an homogeneous solution of water and oil?

texts:
I wondered if in certain condition like very high pressure(so that water and oil remain liquids) and very high temperature(so that the variation of the Gibbs energy is negative--> ∆G = ∆H-T*∆S) we can make an homogeneous solution of water and oil.

Or, alternatively, mixing water and oil meanwhile applying an intense electric field so that the oil molecules get a charge such that they become soluble in water.

Do you think these methods could work? Is there any other way to mix them?


texts: Electrophilic substitution in phenyl alkyl ether

texts:
Phenylalkyl ethers undergo usual halogenation in the benzene ring, e.g., anisole undergoes bromination with bromine in ethanoic acid even in the absence of iron (III) bromide catalyst.

Why do we use ethanoic acid as a solvent? Why don't we use CS2 as a solvent? Does ethanoic acid has something to do in activating phenyl?


texts: How dangerous are non-soluble trivalent thallium compounds?

texts:
I am PhD student in solid state physics. I have been working with a fine powder of a transition metal oxide containing trivalent thallium. The oxide is not soluble in water.

In my university, physicists never learn how to deal with dangerous compounds properly (there's this one guy in my lab who does not believe in wearing gloves...), so I wanted to ask you guys how dangerous you think this compound is.

I'm not dealing with huge quantities of this sample, about 10-100 mg. Perhaps the most dangerous aspect of that particular powder sample is that the grain size is small enough that even the smallest stream of air during sample handling causes a loss of a small amount of powder (= visible grey traces on kimwipes). That probably makes it easy to inhale small quantities without even noticing.

I have occasionally done experiments with that stuff since 2 years now, and I'm not dead yet, nor have I ever noticed any symptoms of thallium poisoning, so I feel like I'm doing fine. I'm just curious how many people I could kill what could happen to me if things go bad (touching the powder with bare skin, inhalation, touching the eye with contaminated gloves because I'm tired, ingestion, etc.)

PS: This is my first time posting on any SE, so if I'm doing it wrong please let me know.


texts: How to determine limiting conductivity of specific ions?

texts:
Given a table with equivalent conductivity of certain electrolytes, how can I determine the conductivity of separate ions? I know that you can find the difference between for example $\ce{K+}$ and $\ce{Na+}$ if you know the limiting conductivity of $\ce{KOH}$ and $\ce{NaOH}$, but how do you calculate the actual value for those two ions?

EDIT:
I've found a different source for the table, my apologies. Let me rephrase my question. Many texts on electrolytic conductivity refer to a table containing the molar conductivity of individual ions, (2). What I'm wondering is, how are these values obtained? Can they be calculated with data from (1)?


texts: What would happen if I added $\ce{Na2CO3 \cdot n(H2O)}$ to a solution of $\ce{HCl}$? Could I consider the reaction the same as just $\ce{Na2CO3 + HCl -> NaCl + CO2 + H2O}$?


texts: Why are the two bonds in sulphur dioxide identical?

texts:
Triatomic molecules are either linear or bent. If we analyse the $\ce{SO2}$ molecule,  it turns out that it is bent.
I know that $\pi$ bonds do not alter shape, but merely the bond lengths.
Now since one of the bonds between S and O is a p$\pi$-p$\pi$ bond and the other bond is a d$\pi$-p$\pi$ bond, the two $\pi$ bonds are not same, so the bond length should not be the same, but my book says the bond lengths are the same which is quite puzzling. I thought maybe its due to resonance but there's no way resonance takes place here.  I read this question,but it don't answer many questions as:
Why d-orbitals of sulphur cannot be used  ?
And  in answer by @Kenny Lau ,
what's specify reason for 'Sulfur sharing two electrons among itself and the other two oxygen atoms.'
So, that makes me think then, what could  be the reason for same bond length in $\ce{SO2}$?
It is not clear as to why d-orbitals of sulphur cannot be used and in the answer to this question @Kenny Lau does not specify reason for 'Sulfur sharing two electrons among itself and the other two oxygen atoms.'


texts: What is the pale green solution from dissolving sodium hydroxide in a stainless steel flask?

texts:
I have previously used drain/sink cleaner gel based on sodium hydroxide but noticed that caustic soda crystals were a lot cheaper.  I decided to experiment with making my own cleaner.

I bought a 1 litre stainless steel flask and placed 500 ml of tap water in it.  Then I added 500 g of caustic soda (from the hardware store) over maybe a 3 hour period.  I stirred it with a new, unpainted wooden spoon.  The solution got very hot!  Then I poured it into a HDPE milk bottle, there was no free solid left and it had all dissolved.  However the solution was pale green!  When we used sodium hydroxide solution years ago in the lab, it was colourless.  Also the end of the spoon which was in contact with the alkali was discoloured to a dark brown.

What is the source of this green?  Is it a chromium compound, having stripped this out of the stainless steel?
The stainless steel flash looks normal, and has been thoroughly rinsed. Is it safe to use for holding tea/coffee?


texts: Chemical equilibrium and Le Chatelier's principle

texts:
$$\ce{energy + 2KClO3 (s) <=> 2KCl(s) + 3O2 (g)}$$

The reaction will be more active in the reverse direction if:

$\ce{O_2}$ is added
more $\ce{KCl}$ salt is added.
More $\ce{KClO3}$ is added
Increasing the temperature.

My thoughts:

I think (1) and (2) are both right. But the book states that only (1) works and I can't find reason for that searching google was useless.

$K_c = [\ce{O2}]^3$, so if we increased $\ce{KCl}$ or decreased $\ce{KClO3}$ it won't affect the equilibrium?

$$\ce{Fe(OH)(s) <=> Fe^{2+}  + 2OH^-}$$ The reaction will be more active in the reverse direction if : ... is added

$\ce{KOH}$
$\ce{Na_2S}   $
$\ce{Fe(OH)_2}  $
$\ce{Fe(NO3)2}$

Won't it be (1) and (4)? The book says it's (4) only.


texts:
I was preparing for an exam and I saw one question which is difficult to understand:

  The electronic configuration $\mathrm{(1s)^2(2s)^2(2p)^6}$ does not belong to:

  a) any element
  b) anion
  c) cation
  d) a transition metal in its ground state
  e) noble gas in its ground state

According to me its (e) because of helium since it electronic configuration is $\mathrm{(1s)^2}$.


texts:
I recently conducted an experiment where I electrolyzed a solution of sodium chloride. I was using a copper coin as the anode, and I observed a pale blue precipitate in the cup when I was done with the experiment. I then deduced the following:

The chloride ions get oxidized at the anode:

$$\ce{2Cl- -> Cl2 + 2e-}$$

The chlorine gas then reacts with the copper anode to form copper(II) chloride which goes into solution as it is completely soluble.

At the cathode, the hydrogen in the water gets reduced to form hydrogen gas:
$$\ce{2H2O + 2e- -> 2H2 + 2OH-}$$

I know the above half reactions exist from the list of standard reduction potentials.

Next, the copper(II) ions react with the hydroxide ions being formed to produce copper(II) hydroxide, which is both insoluble and pale blue.

However, this source mentions that the hydronium ions in the water get reduced at the cathode:

$$\ce{2H+ + 2e- -> H2}$$

Is this correct? In my understanding, the concentration of hydronium ions ($\pu{1e-7 M}$) would be much too low, and where would the hydroxide ions come from to form copper(II) hydroxide?


texts: Synthesis of synthetic detergent with Friedel Crafts Acylation

texts:
I propose the following synthesis.

Oxidation of aldehyde to a carboxylic acid. This sets me up for FC acylation once I ...

Attack the -OH with thionyl chloride ad form the acid chloride.

Reaction with vanilla benzene in the presence of Lewis acid catalyst. Benzene won't go after acid chlorides unless there is some catalyst in the system.

Now that the acid chloride is installed, I can go through the motions of getting rid of the pesky C=O group.

Given that alkyl groups are slightly activating and are ortho/para directing, I can sulfonate with fuming sulfuric acid and expect a mixture of products (including the one desired by the synthesis). Sterics might favor the para product over the ortho product given the sheer size of the SO3 group.

General comments:
I did NOT sulfonate first, as that is an electron-withdrawing group akin to the nitro group. It deactivates the ring and is also a meta-director. I want a para-substituted product. Not a meta-substituted product.
Therefore, how reasonable is my synthesis? Is it correct?
Also would sulfonation before getting rid of the C=O work? Something tells me no; the C=O is able to withdraw electrons from the ring via resonance, and that would make it a meta-director.


texts: Is propane-1,2,3-tricarbaldehyde the correct IUPAC name of CHO-CH2-CH(CHO)-CH2-CHO?

texts:
We were asked this question in class:

  What is the IUPAC name of the compound $\ce{CHO-CH2-CH(CHO)-CH2-CHO}?$

I don't know for sure, but I think the answer should either be 3-formylpentan-1,5-dial or 2-(formylmethyl)-butane-1,4-dial. However, I am told that the correct answer is propane-1,2,3-tricarbaldehyde.

How can that be? I searched on the internet and found that we use 'carbaldehyde' as the suffix only when the $\ce{-CHO}$ group is attached to a ring. But here the given compound is an open chain compound, so I don't see why we're using 'carbaldehyde' as the suffix.

My course textbook mentions that this compound is named so "to give identical treatment to all aldehydic groups". But I haven't learnt that such a rule exists in IUPAC nomenclature.

What is the correct name of this compound and why?


texts: How can I increase the viscosity of dilute hydrochloric acid

texts:
I'm cleaning the mortar off a new clinker brick wall. Walls actually. I hate this job. The builder told me to wash down the wall with weak HCl, leave it for a minute or two, and then spray it off with a pressure hose (eg Kärcher or Gerni). There are lots of problems with this. The main one is that the HCl gets painted on with a coarse bristled brush and splashes everywhere you don't want it to be. The protective clothing is a huge impediment to being able to do the actual job. The safety eye protection fogs up and you can't see how well you've cleaned. Once the bricks are wet, the mortar residue becomes transparent, so it looks clean, only to dry out and turn white again. Then there's the problem with blasting weak acid all over the place. I really hate this job.

So I was thinking that in order get some control over the application of the acid, it would be great if it was the consistency of paint. Then I could apply to only those areas that it needs to be. Question is, how do I make my dilute HCl the consistency of paint? Please feel free to correct me if viscosity is not the right word.


texts: Why do full shell ions such as chloride form coordinate bonds, while noble gases do not?

texts: Both $\ce{Cl-}$ and noble gases have full outer shells, why does $\ce{Cl-}$ react whereas the noble gases mostly don't?


texts: Why are alpha-carbonyl relatively less stable?

texts:
So if we have an alpha halogen ketone, why is an Sn1 type mechanism so unfavorable for that species?

I don't understand. It seems like the C+ would be resonance stabilized by the carbonyl's double bond.


texts: Clarification on absorption spectra and crystal field theory

texts:
My textbook, Chemistry: The Central Science, gives this figure to explain the purple color of the hexaaquatitanium(III) ion:

Such absorption spectra are common to chemistry and biochemistry. However, as the crystal field theory explains, the peak wavelength absorbed is equal to the splitting energy $\Delta$ between the two split energy levels of the d subshell. This is illustrated in the figure below.

So the splitting of the d subshell explains the peak of the absorption spectrum. However, I’m not comprehending why the curve slowly descends on either side of that peak—if only 495 nm light is absorbed, then shouldn’t the absorption spectrum show absorption only at 495 nm, with no absorption anywhere else? Why does absorption slowly decrease as you move in either direction away from 495 nm? What mechanism allows these other wavelengths to be absorbed as well?

Moreover, normally, when things absorb light, they reemit the energy in the form of infrared. That’s why that wavelength is taken out of the wavelengths that reflect back to your eyes; if the same wavelength were reemitted, you would perceive it too. I assume infrared is radiated because electrons can take alternate pathways to move back to ground state, jumping down in small steps that release less energy each time. However, with d subshell splitting, there is only one possible way for the electron to climb down to ground state. Shouldn’t that mean that the wavelength it absorbed will be reradiated out? Shouldn’t we see that wavelength, then?


texts: Freeware that converts structure in a conformational model?

texts:
In order to draw chemical structures I use ChemBioDraw Ultra.

As an exercise I've to draw the most stable conformation.

I expect a twist-boat like structure (instead of usual chair conformation for substituted dioxanes)

Is there a freeware or an easy computer online tool to check if my propose (right side picture) is correct?

When I go to >Edit > Get 3D Model the program gives me a small picture with a 3D-Model:

By double-clicking this small image it opens ChemBio3DUltra and I can rotate this molecule:

@Martin: Is this correct (I've expected a twisted cyclic ring)?

@Martin I draw the structure at right with i-Bu and H exchanged in Chemdraw and do >Edit > Get 3D Model

The reason why I first thought it should be twist boat like was that one C-O is pointing up and the other pointing down. May be someone knows why people gives this stereoinformation inside the cyclic ring?

As I've drawn it as a twist boat I get exactly the same with ChemBioDraw. Is there a way to calculate by how many kcal/mol the first one is more stable then the second one with ChemBioDraw?

What's interesting: I searched for a structure in which the twist-boat conformation is the most favorable one and found one:

  However, when there are two large substituents in the cis-1,4 arrangement on
  a cyclohexane ring, neither of which will go easily into an axial position, then
  it appears that the twist-boat conformation (Section 12-3A) is most favorable
  [http://authors.library.caltech.edu/25034/13/BPOCchapter12.pdf, page 458]

(The A-value of a tert-Butyl is in the range of 5 kcal/mol which is around the value of the energy difference between cyclohexane in twist-boat and chair conformation.
I've drawn cis-1,4-di-tert-butyl-cyclohexane with ChemDraw and used >Edit>Get 3D Model and ChemBioDraw gave me the structure which is NOT the energetical most suitable one! Why?


texts: Is there an all-natural, non-volatile and low viscosity oil?

texts:
The goal is to thin a vegetable oil so that it spreads easily on top of water. It is not for consumption and the flash point of the mixture should be >=95° Celsius". Vegetable oils tend to have flash points greater than 225° Celsius so the flash point of any additives can be well below 95°, as long as special precautions would not be necessary in a manufacturing process.

Since my original post, I've discovered another reason for the low viscosity. It is required for the delivery system to work properly.

I am open to other means to achieve the goal.


texts: Calculating time taken for a set percentage of a reaction to occur based on half-life

texts:
The half-life of a first order homogenous gaseous reaction: $\ce{SO2Cl2 -> SO2 + Cl2}$ is 8.0 minutes. How long will it take for the concentration of $\ce{SO2Cl2}$ to be reduced to 1% of the initial value?

I solved it this way:

Let initial mass be 100, so that the final mass is 1.
$$100 \cdot (\frac{1}{2})^n=1$$
I solve this for n, and multiply it by 8.0 to get the time taken.

Answer is spot on, and the method is identical to the one used in half life questions in Physics. Yet my Prof insists that I solve for the rate constant first, and then find half-life from that, and that my answer is wrong because n, the value for number of half-life periods, cannot be a decimal value.

The questions I found online all explicitly ask for the rate constant, which the question I got doesn't ask for.

Is my method right/wrong? Can you guys provide proof?


texts: Calculation for buffer of pH 5 in sodium fluoride solution

texts:
From a journal:

  $\pu{500 mL}$ of $\pu{50 ppm}$ fluoride at $\mathrm{pH}~5$ was prepared by mixing $\pu{0.0552 g}$ of sodium fluoride with $\pu{4.1057 g}$ of sodium acetate and $\pu{1.65 mL}$ of acetic acid.

May I know how to get the solution of calculation for amounts of sodium acetate and acetic acid which are $\pu{4.1057 g}$ and $\pu{1.65 mL}$, respectively?

For sodium fluorid calculation is

$$\frac{\pu{50 mg}}{\pu{1 L}} \times \frac{\pu{1 g}}{\pu{1000 mg}} \times \frac{\pu{41.98 g mol-1}}{\pu{18.988 g mol-1}} \times \pu{0.5 L} = \pu{0.0552 g}$$


texts: What will happen to the entropy and free energy of the gasses when the partition is removed?

texts:
Consider a container of volume $ 5.0$  L that is divided into two compartments of
    equal size. In the left compartment there is nitrogen at $1.0$ $atm$ and $25 °C$; in the
    right compartment there is hydrogen at the same temperature and pressure. What
    will happen when the partition is removed?

  $A) $The entropy decreases, and the free energy decreases.
  $B)$ The entropy increases, and the free energy decreases.
  $C) $The entropy increases, and the free energy increases.
  $D) $The entropy decreases, and the free energy increases.

Logic tells that upon removing the partition, randomness increases and hence entropy increases. I am confused about free energy. First law of thermodynamics has to be applied , I think. But I can't seem to get the right direction.


texts: I have to distinguish between copper oxide and carbon. I thought of dilute sulfuric acid because it forms copper sulfate with copper oxide. But I don't know how carbon reacts with dilute sulfuric acid. I know how carbon reacts with concentrated sulfuric acid but dilute?


texts: Why does thallium hydroxide increase the yield of product in a Suzuki reaction?

texts:
I came across a research paper by Uenishi et al. [1] where relative rates of $\ce{KOH}$ and $\ce{TlOH}$ in Suzuki coupling reactions are compared.

Thallium hydroxide increased the yield of products, see Table I below. The reaction also occurred at room temperature as compared to $\ce{KOH}$.
What is the effect of thallium hydroxide?

References

Uenishi, J.; Beau, J. M.; Armstrong, R. W.; Kishi, Y. Dramatic Rate Enhancement of Suzuki Diene Synthesis. Its Application to Palytoxin Synthesis. J. Am. Chem. Soc. 1987, 109 (15), 4756–4758. https://doi.org/10/fhmqsr.


texts: Why are protic acids not used for the formation of thioacetals?

texts:
The standard procedure for protecting a carbonyl group as an acetal uses dry acid, such as $\ce{TsOH}$, but when forming a thioacetal, the Lewis acid $\ce{BF3}$ seems to be the catalyst of choice. For example, see Corey and Seebach's original demonstration of dithiane acidity: Org. Synth. 1970, 50, 72.

Is there any particular theoretical or practical reason why this is the case? I am guessing that the boron trifluoride coordinates exclusively to the harder oxygen atom, making it a better leaving group and hence favouring the formation of products (since the reaction is under thermodynamic control). However, I don't see any reason why acid wouldn't be able to do the job equally well.


texts:
This reaction proceeds in the galvanic cell:

$$\ce{Zn + Pb^{2+} -> Zn^{2+} + Pb}$$

I need the equation for the half-reactions of this cell and the theoretical voltage produced by this cell if concentration of $\ce{Zn^{2+}}$ is $\mathrm{0.1\ mol/L}$ and concentration of $\ce{Zn^{2+}}$ is $\mathrm{10^{-4}\ mol/L}$.


texts:
I need help sorting out the molecular structure of tri-lead tetroxide, aka lead(II,IV) oxide $\ce{Pb3O4}$.

This data sheet shows this image:

The Wikipedia's lead (II,IV) oxide's link to a Jmol interactive image looks like this:

Even the Wikipedia article's Talk Page's discussion on the naming and structure makes for interesting reading.

The first drawing shows a $\ce{Pb-O-Pb-O-Pb-O -}$ ring, the second shows a 4-bond $\ce{Pb}$ in the middle with two 2-bond $\ce{Pb}$'s on either side.

Is there a "right way" and a "wrong way" to draw a single molecule of $\ce{Pb3O4}$ that represents how it might actually be configured? Are both, either, or neither of the above representations "right"?


texts: Reduction of α,β-unsaturated nitro compounds

texts:
Would it be possible to reduce a α,β-unsaturated nitro compound to a saturated amine using for example $\ce{NaBH4}$? I know these kind of compounds will be reduced by hydrogenation using a $\ce{Pt/C}$ catalyst, $\ce{LiAlH4}$ or freshly prepared Raney Nickel, but I'm looking for a reducing agent that is easier to handle than those.

The book from which I'm learning, Clayden et al., does not really go into much detail on reduction of nitro compounds or unsaturated alkanes, other than that hydrogenation is a good approach to both and that the nitro group is one of the most easily reduceable functional groups. But how about a α,β unsaturated compounds then? How would I asses whether some reducing agent is able to reduce both simultaneously?


texts: How to determine the source of sub-nm periodic error in NIR spectra

texts:
I've run into an issue collecting measurements on deionized water in the $1050-\pu{1200 nm}$ range. To determine the sensitivity of my spectrophotometer in this range, I've acquired measurements on pure deionized water in double-beam mode using two identical quartz cuvettes. I have taken measurements at several time steps near $\pu{1064 nm}$, from $0.1-\pu{100 s}$ per time-point and constant $\pu{0.1 nm}$ per step and $\pu{2 nm}$ bandwidth. I keep finding that the baseline standard deviation (SD) does not improve beyond $1.4 \times 10^{-4}$ Abs.
This value is technically below the acceptable qualification values of $2 \times 10^{-4}$ Abs in that range, but I'm trying to determine if this is the ultimate noise level of the instrument in this range or if these periodic variations are due to a mechanical issue in the monochromator like a lead screw, or due to environmental or electrical line noise of some kind.

Any thoughts are appreciated.


texts: Do cyclic oxygen molecules exist and their theoretical stability?

texts:
Do oxygen molecules ever become cyclic shapes like carbon and other elements?

Why doesn't oxygen form cyclic compounds? How stable would they be if they do exist. Especially more than 3 oxygens. Why are there just 2 allotropes of oxygen known to mankind.


texts: What are the physical manifestations of radial nodes?

texts:
I realize that nodes (both angular and radial) are areas with zero probablility of finding an electron.  I realize that plotting the square of the radial eigenfunction for an orbital will give the probability density of finding an electron at a given distance from the nucleus.

So for the 1s orbital (zero nodes), the graph of the square of the eigenfunction will be one hump.  For the 2s orbital (one node) there will be a small hump followed by a large hump with a zero point in between them (talking about the sqaure of the eigenfunction not the eigenfunction itself).

For the 1s orbital, the peak of the hump will represent the most probable radius the electron will be found from the nucleus.  The probability will lower as the radius increases or decreases from the most probable radius (similar to gaussian distribution), and the electron will have zero probability of being found within the nucleus of the atom (0 radius).

And from what I understand the radial node(for the 2s orbital) is physically manifested at the point where the 1s orbital and 2s orbital meet (my instructor used the analogy of russian nesting dolls), and on the NON squared eigenfunction plot of the 2s orbital, the node is represented where the wave function crosses the x axis going from +y to -y.

So here is what Im really wondering (please correct me on anything stated previously if I am mistaken).  Is the first (smaller) hump on the squared radial eigenfunction (probability density function) for the 2s orbital the probability that the electron is in the 1s orbital (I believe this would be called an excited state if im not mistaken)?  This would make the most sense to me, as it would be saying that it is possible for a 2s electron to be in either the 1s orbital or 2s orbital, but not in between (where the wave function goes from +y to -y)

Edit: Perhaps it is incorrect to say an electron from the 2s orbital has the possibility of being in the 1s orbital.  What I really mean is the electron may occupy the same space as the 1s orbital, but since orbitals are just 3d areas where an electron is most likely to be found perhaps I am not incorrect in saying that a 2s electron occupies the 1s orbital since the 1s orbital is technically just a region in space.  My guess is that the probability of a 2s electron occupying the same space as the 1s orbital is lower than it occupying the space of the 2s orbital due to repulsion by the electrons that already occupy the 1s orbital.

Here is a picture representing everything ive tried to explain so far:


texts: How to recover C18 column after prolonged exposure to phosphate buffer?

texts:
A colleague of mine who occasionally does HPLC in a biochemistry lab discovered that a C18 column was not properly flushed after the previous experiment.
It appears that the column was stored for several weeks capped with aqueous phosphate buffer inside.

The main concern is partially crystallized phosphate as well as bacterial growth as there is no clear evidence whether antibiotics were added to the buffer or not.

Is there a way to recover the column, and if so, what procedure is typically recommended (solvents, temperature, flow rate etc., preferably with a reference for the lab report)?


texts: Why does oxidized copper turn green? I am sorry if this question is too basic, but am really stumped here. It would be helpful if one could provide a research paper or website with your answer.


texts: How were urolithins discovered and named?

texts:
Urolithin is a product of the degradation of ellagic acid by gut flora and has significant biological activity. (Wikipedia)
I am curious as to how it was discovered but cannot find the story. Although I can imagine how it might have been discovered through the study of fecal flora, I cannot imagine why it was named with reference to kidney stones.


texts:
I'm working on solution of Hartree-Fock equation for Beryllium in configuration $1s^2 2s^2$, expanding the orbital with STO-3G basis
$$\phi_k=\sum_{p=0}^3 C_{kp}e^{-\alpha_{kp}r^2}$$
I know the values of $\alpha_k$ both for 1s and 2s.
All books speak about solving molecules and the only case with atom is the helium case, so I have some doubts. In molecular case they expand the molecular orbital as
$$\phi_k=\sum_{p} C_{kp}\chi_p$$
without index $k$ on $\chi_p$ and so also all matrices I need to solve the eigenvalue problem. For this reason I can't understand the difference between the basis set used in molecular case and atom case and consequently how to solve the Fock equation in the case of an atom, and in particular of Beryllium.


texts: Oxidation State in Tetraaquadichlorochromium(III) chloride

texts:
$\ce{[Cr(H2O)4Cl2]Cl}$, Tetraaquadichlorochromium(III) chloride

According to a book, the (III) indicates the oxidation state of chromium, but it doesn't explain why. Cr has 6 valence electrons. How does it get to +3?


texts:
I need to calculate total dissolved solids (TDS) of various groundwater samples from chemical analyzes. I have concentrations of ions/molecules in mg/L. I’ve found various formulas to calculate TDS but the ions/molecules I have never match.  I don’t have a lot knowledge in chemistry.

Here are the three equations I have found. (As i said, I found many different equations and I don't know which one I should use):

Eq. 1 : TDS=Na(+) +K(+) +Ca(2+) +Mg(2+) + Fe^(2+) +HCO3(-) +Cl(-) +SO4(2-) +NO3(-)

Eq.2 : TDS=0.6*Alkalinity (as CaCO3) +Na(+) +K(+) +Ca(2+) +Mg(2+) +Fe(2+) +Cl(-) +SO4(2-) +NO3(-) [1]

Eq.3 : TDS=cations +anions +SiO2

Problems/questions I have:

•I don’t have the concentration of HCO3(-).

•I have the concentration of CaCO3. In natural waters, alkalinity (mg/L CaCO3) is HCO3(-)+CO3(2-) +OH(-) +H(+). At pH under 8.3, could I simply convert the concentration of CaCO3 in HCO3(-)? If yes and if the pH is over 8.3, is there a way to calculate the concentration of both HCO3- and CO3(2-)?

•I don’t have the concentration for NO3-. I only have the concentration for NO3-+NO2. Is there a way to isolate the concentration of NO3(-)?

•I don’t have the concentration for SiO2. I only have the concentration for Si. Could I simply use the concentration of SiO2?

•The pH of my water samples varies from 6 to 9.

•Also, I don't have the samples so I cannot titrate the water or measure electrical conductivity.

Thank you!

References:

[1] Federation, W. E., & American Public Health Association. (2005). Standard methods for the examination of water and wastewater. American Public Health Association (APHA): Washington, DC, USA.


texts: Amount concentration versus number concentration

texts:
The IUPAC Gold Book defines

Amount concentration
Amount of a constituent divided by the volume of the mixture. Also called amount-of-substance concentration, substance concentration (in clinical chemistry) and in older literature molarity. For entities B it is often denoted by B. The common unit is mole per cubic decimetre or mole per litre sometimes denoted by M.

and

Number concentration
Number of entities of a constituent in a mixture divided by the volume of the mixture.

I can't see a distinction between the two terms since it seems to me that "Amount of a constituent" is the same as "Number of entities of a constituent".
Could you please explain the difference between them? Is it a conceptual difference or just a difference in the context in which they are most commonly used?


texts: Why do coefficients become exponents in the speed equation when dealing with elementary reactions

texts: In school, while studying chemical kinetics, we were learning about the speed law and equation for different chemical reactions. We learned that in general, the exponents of the concentration of reactants in the speed equation must be determined experimentally. However, earlier this week, we learned that if we are talking about basic elementary reactions, the coefficients of the reactants become the exponents in The equation. This puzzled me. Can anyone explain why the coefficients would become exponents? Thanks in advance


texts: Thermodynamic versus kinetic reactions 2

texts:
I want to ask more following the previous Question. (Thermodynamic versus kinetic reactions)

in this reaction below, is the first product 'kinetic product'? and second one is 'thermodynamic product' ?
upper pathway is acid/base reaction but doesn't seem reversible, thus looks like far from thermodynamics. but I learned acid/base reaction is about thermodynamics. what did I get wrong?

I'd appreciate any comments^_^


texts:
$$\ce{Fe2O3 + 6HI -> 2FeI2 + I2 + 3H2O}$$

Why don't we get $\ce{FeI3}$? After all, iron's oxidation state is $+3$ in the reagent.

Should one just memorize that up to bromine, it's $\ce{FeX3}$, and below it's $\ce{FeX2}$?


texts: Finding the value of stoichiometric coefficient x

texts:
$\ce{2A_{(s)} + xB_{(g)} <=> 3C_{(g)}}$

$\mathrm{K_p}=19.3, \mathrm{K_c}=0.45, \mathrm T=523\pu K$

I work $\Delta n$ to be $1$, So would $x$ be $1$ or $2$? I'm not sure if the coefficient is part of $\Delta n$.


texts:
On the web there are tons of different recipes for a solution to make soap bubbles.
Most of them use only three ingredients:

water
dish soap
glycerin

But their ratios widely change among the sources.
Right now I'm using: 20:5:2 in volume.

The bubbles come out, but not as I desire.
Compared to a commercial solution, mine are bigger but last shorter. End if I constantly blow with some strength, the commercial solution produce literally hundreds of small bubbles (diameter between 1 and 4 cm), while mine will just make a couple of middle-sized bubbles and then the membrane will break.

The goal is to make a solution that allows to:

make big bubbles if the blow is weak
make a lot of small bubbles if the blow is strong
maximize the duration of the bubbles

I will appreciate any hint in this direction, but I'm also interested to understand how to tune the ratios of the 3 ingredients. I mean, given the requirements above (I guess they are the most common!) how would you calculate the ratios?

Of course I can experiment. But I want to learn the theory behind.


texts: Conjugate addition vs Electrophilic addition

texts:
I was just doing an organic chemistry problem from an online source recently, on the topic of conjugate additions (or 1,4-additions). Below is an image illustrating the problem.

I chose the upper route while the solution manual claims that the answer is the lower route. My rationale for choosing the upper route was that perhaps the alkene is not nucleophilic enough to react feasibly in an electrophilic addition with $\ce {HCl}$. This is due to the presence of the electron-withdrawing carbonyl. Thus, it is important that we first get rid of the carbonyl by using the ethyl Grignard. Then, we can easily add the $\ce {HCl}$ for the electrophilic addition.

Upon reconsidering my reasoning, perhaps I was too narrow-minded in saying that the $\ce {HCl}$ must add in the fashion of electrophilic addition. Perhaps, conjugate addition could also take place. And also, by choosing the upper route, I cannot assure that my chlorine atom would end up in the desired position due considerations of the stability of the carbocation intermediate. Thus, I agree that my choice is incorrect.

The correct choice is the lower route and this does ensure that the $\ce {Cl}$ is in the right place in the final product, as it adds via a conjugate fashion. But how is the writer of the solution so sure that the $\ce {HCl}$ would add in a conjugate fashion, instead of via an electrophilic addition?


texts: Mathematics in inorganic and quantum chemistry

texts:
Is mathematics important to learn concepts in inorganic chemistry, such as point groups, point symmetry, because doing these topics requires one to determine the symmetry of the elements and to visualize 3D (such as determining the symmetry of a water molecule?)

As these concepts are derived from mathematics, I wonder whether taking maths courses would be helpful for me to understand these concepts better and if so which maths course would be most useful? Such as linear algebra, abstract algebra?


texts: When hypochlorous acid is dissolved in water, is it the chlorine atom or the oxygen that serves as the anti microbial agent?


texts: What difference does a polar protic solvent make in the addition of X2 to alkenes?

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After the formation of the cyclic intermediate, $\mathrm{S}_{N}2$ reaction takes place. This reaction would be favored by an aprotic solvent.

How will the products of the reaction be affected if I use a polar protic solvent?

I think that the formation of the cyclic intermediate is independent of the solvent used but I can't figure out what would happen after that.


texts: What is the purpose of UV-VIS Spectroscopy?

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I understand the purpose behind infrared spectroscopy and mass spectroscopy, but UV-VIS doesn't make much sense to me.

Through research, I see that it has to do with electron orbitals, and it has a relation to Beer's Law.

But what exactly can I learn about a molecule from its absorbance/transmittance of UV/Visible light?


texts: Is it possible to make graphite an insulator?

texts: Since graphite is anisotropic electrical conductivity, won't it be possible to make it an insulator instead? Like manufacturing it such that the plates of carbon atoms are mostly parallel to one another.


texts:
I know basic cell representations of galvanic cells and can identify the anode/cathode. But here's a weird representation that I encountered and couldn't understand it:

$$\ce{Pt | H2(g)}(\pu{1.0 atm})\ce{ | HX || KCl(1M) | Hg2Cl2(s) | Hg | Pt}$$

What does this actually translate into?


texts:
I have a mixture of $\ce{NO2(g)}$ and $\ce{N2O4(g)}$ at $63\ \mathrm{^\circ C}$ and $750\ \mathrm{mmHg}$. I need to find the weight percent of the first compound. Density $d=1.98\ \mathrm{g/L}$.

I assumed that we have $M=aM_1+bM_2$ where $M_1$ and $M_2$ are the molar masses of the first and second compound. I know that $m=nM$ so the weight percent would be $$\frac{m_1}{m}\cdot100\ \%=\frac{aM_1}{aM_1+bM_2}\cdot100\ \%$$
My problem lies in finding the coefficients. Can someone give a hint please?


texts:
I understand that acetanilide can hydrolyze to aniline and assume that will happen if that gets added to an aquarium, thus causing toxicity?

I have a solution that is $3\%$ hydrogen peroxide and $0.25\%$ acetanilide that I'd like to add to my fish and shrim aquarium to kill some algae.


texts: Flame Test Spectrograms Not Lining Up With Reality

texts:
In my AS Level chemistry class we had tried some DIY spectroscopy of flame tests with the aim of identifying anions in certain salts. We got as far as building the spectrometer inspired by Paper Craft Spectrometer (though we built a much bigger version such that a DSLR could be used) and performing the experiment and collecting the data. The problem was that I couldn't manage to get many of the spectrograms to line up with those sourced from the web. Many of our spectrograms, while plenty bright and with lines covering the whole visible range, had too few lines and those that were there didn't align with any real data we could find.

For instance with the following recorded spectrogram:

Some processing was done on the above image to produce the spectrum below it. The scale is calibrated from an LED which was also recorded and then confirmed my matching it against the emission of sodium which also roughly lined up to this scale +-10nm. From the colour of the flame we assumed it was calcium, given that all salts tested were chlorine salts, and the metal is one of: Ca, Cu, Cs, K, Li, Na, Sr. I don't know if there was an experimental error or if we were not looking at the correct reference spectrograms but nothing I could find would line up with that,does anyone have any insight into this?