texts: Changes in defects in a material due to heat treatment

texts:
Currently i am doing some research on optical properties of  a oxide material and for that purpose i have done some photoluminescence study on it. Because this is an ongoing research i cant divulge much information here. I have used "$Ex$" excitation wavelength for getting emission spectra for my oxide sample. I have prepared two types of oxide samples one is heat treated and the other not heat treated. After taking emission spectra data for both the samples I got peaks similar to this

Samples               Peak wavelength (nm)

Non Heat treated          a, b

Heat treated              b,c,d,e

*a,b,c,d & e are wavelength where emission peaks detected

Both samples (heat treated and non heat treated) has same chemical composition which i confirmed using powder XRD. As you can see from the data the heat treated sample has more emission peaks comparing to non heated samples. I can understand from this data that heat treatment to the sample causes increased defects in the sample. what i thought was that after heat treating a crystalline material; the defect in that material should decrease and not the other way round? Is my rationale wrong. Why heat treated sample has more defects?


texts: Molar conductivity of coordination compound

texts:
The compound is $\ce{[Cr(H2O)6]Cl3}$. Which isomer has least molar conductivity ?
Correct answer : $\ce{[Cr(H2O)4Cl2]Cl.2H2O}$
My answer : $\ce{[Cr(H2O)3Cl3].3H2O}$
Molar conductivity is directly proportional to the number of ions on dissociation. If number of ions is same, the one with more net charge  has more molar conductivity. Therefore the compound I stated should have least molar conductivity as the only dissociation it undergoes is separation of coordination entity from water molecules. As none of them are charged ions, they wont increase molar conductivity. What is wrong with my concept ?


texts: Detailed kinetic explanation for vapor pressure reduction by dissolved solute?

texts:
The following problem was asked in JEE Mains 2020 (Sept 2, Shift 1),

An open beaker of water in equilibrium with water vapor is in a sealed container. When a few grams of glucose are added to the beaker of water, the rate at which water molecules:
(A) leaves the solution increases
(B) leaves the solution decreases
(C) leaves the vapor increases
(D) leaves the vapor decreases

According to the NCERT for Class XII, Part I, pg. 46, para 3,

In  a  pure  liquid  the  entire  surface  is occupied by the molecules of the liquid. If anon-volatile solute is added to a solvent to give  a  solution  [Fig.  2.4.(b)],  the  vapor pressure  of  the  solution  is  solely  from  the solvent  alone.  This  vapor  pressure  of  the solution at a given temperature is found to be  lower  than  the  vapor  pressure  of  the pure  solvent  at  the  same  temperature.  In the solution, the surface has both solute and solvent molecules; thereby the fraction of the surface covered by the solvent molecules gets reduced.  Consequently,  the  number  of solvent molecules escaping from the surface is correspondingly reduced, thus, the vapor pressure is also reduced.

So, after reading the last lines of above quoted text, I think that the vapor pressure is reduced, because the rate at which solvent molecules leaves the solution decreases, due to a decrease in exposed surface area. So, acc. to me option (B) should be correct. But, it was incorrect, acc. to the key.
Is there anything else, I'm missing?

The answer given is,

 (C) leaves the vapor increases


texts: Ionization enthalpy for group 13 elements

texts:
The ionization enthalpy for elements along a group generally reduces.
  But there is an exception for group 13 elements and the order is not
  uniform.

  The order is:
  B>Tl>Ga>Al>In

According to my textbook, the reason for this is the weak screening effect of electrons in d and f orbitals.
What does this mean?

The following is from the textbook i referred:

  The ionization enthalpy values as expected
  from the general trends do not decrease
  smoothly down the group. The decrease from
  B to Al is associated with increase in size. The
  observed discontinuity in the ionization
  enthalpy values between Al and Ga, and
  between In and Tl are due to inability of d- and
  f-electrons ,which have low screening effect, to
  compensate the increase in nuclear charge.

Source


texts: What is the role of the slash ("/") in chemical reactions?

texts:
I have always been confused about the role of slash in chemical reactions.

In some reactions, e.g. $\ce{NaBH4}/\ce{OH-}$ it means we use both compounds, right?

And in reactions where we write $\ce{Pt/Pd/Ni}$ do we mean platinum or palladium or nickel?


texts: Development of experiments to optimize HPLC-MS procedure using 2D central composite full factorial design

texts:
I have recently been studying development of experiments and how to statistically plan/optimize an experiment for x number of variables based on y number of responses.

To begin with, I am just going to use a 2D central composite full factorial design (CCD) to make sure I don't screw up bigger designs later. My two factors are 'load pH' and 'load conductivity'. My min/max values will be 6.5 - 7.5 and 5.5 - 6.5 respectively. My alpha value = sqrt(2) and I have scaled my model so far to (from min to max):

$$
-\sqrt{2}, -1, 0, +1, \sqrt{2}
$$

In a 2D CCD where 9 experiments are needed (depending on number of centre points), what relevance are the -1 and +1 values? To clarify, if my 2D array is effectively a 3x3 grid then the x and y axis will respectively read $-\sqrt{2}, 0, +\sqrt{2}$. What is the purpose of -1/+1?


texts: Can organic acids be concentrated and used like concentrated sulfuric acid and similar mineral acids?

texts: Is it possible to make organic acids concentrated like inorganic acids like concentrated sulfuric acid and similar mineral acids?


texts: Oxygen or carbon with a positive charge? (comparison of canonical structures)

texts:
Which of the contributing structures of the resonance is more stable?

I'm watching a video lecture by a professor of my college where he puts this question to the class. The class unanimously says B. At first I thought they were wrong, but then the professor agreed with them.

Is this true? The reason he gave was that oxygen's octet would be complete in B, hence it contributes more. But I don't understand this.

1) Isn't the octet complete in A too? It has 2 covalent bonds - 4 electrons (2 from sharing) and 2 lone pairs. Adding up to 8.
2) Oxygen being more electronegative than carbon, would pull the electrons towards itself, leading me to think that it would be more comfortable with a lone pair rather than another bond. Also, won't it prefer to lose out that '+' charge which the bonding's burdened onto it?

Am I wrong?

Another thing which made me believe that Prof. may have made a mistake while talking about the more relevant contributor, is that when he added Br$^-$ to the compound, he added it to the canonical structure A. And don't you explain reactions with the most relevant contributor, i.e. B?

Answer

The presence of an extra bond in the canonical structure B, along with the completion of the carbon valency makes it more stable than A. The reaction with Br$^-$ is best explained looking at A, though, because the incoming nucleophile ends up bound to carbon, not oxygen.
Thanks, everyone!


texts: Which species gives electron in the following reaction?

texts:
In a given reaction like this:
$$\ce{FeO4^2-  + 3e^-  + 8H+ <=> Fe^3+ + 4H2O}$$

From where does the electron come  in the acidic medium, as there is no other species to get oxidised in the medium? Also if this were in basic medium then why there is no oxidation of any other species in the medium?


texts: Problem with synthesis of calcium formate

texts: I just tried preparing calcium formate by adding $\ce{Ca(OH)2}$ to ammonium formate, but I observed no bubble formation and no smell of ammonia. Why doesn't calcium hydroxide, being a strong base, displace ammonia?


texts:
I am seeking an isotopic composition database for carbon isotopes, since I would like to make a figure showing the different isotopic compositions of different materials. The best woudl be if the values are given as $\delta$ values versus the international VPDB-scale (VPDB=Vienna Pee Dee Belemnite)
I already did some research but I only coudl find figures not the raw data, and extracting the data from figures is tedious and not that accurate. Is there any data base, that lists ranges and also the literature? What I have found so far is for example, all values are on the VPDB scale.
"marine carbonates" -6‰ to 4‰
"atmos. CO_2" -8‰  to -7‰


texts:
If you know the composition of any sample of compound, is it possible to predict it's flame test color?

For eg, if you can given Sodium Chloride, then without actually doing the flame test, can you mathematically (and using physics and chemistry obviously) come up with it flame color, ie yellow-orange?

Do the flame test colors follow any pattern for different metals? (for eg, does it follow the spectrum?)

Does the group (for eg alkali metals or transition metals) affect the flame color?


texts: I have to write a Python program relating with molecular weight. Any insight?

texts:
Write a program that determines the molecular weight of a chemical compound based on the number of hydrogen, carbon, and oxygen atoms in the compound. You should use the following atomic weights:
  \begin{array}{|c|c|c|c|}
\hline
\text{Atom} & \text{Weight}~\pu{gm/mole} \\\hline
\ce{H} & 1.0079 \\\hline
\ce{C} & 12.011\\\hline
\ce{O} & 15.9994\\\hline
\end{array}

I don’t understand the relation between molecular weight and the number of $\ce{H}$, $\ce{C}$, and $\ce{O}$.

The professor has said "there is no need to be able to handle chemical compound names like $\ce{H2O}$ or $\ce{C2H5OH}$. (I plan to discuss how to handle these later in class) Instead, the user should just be asked to specify the number of hydrogen, carbon, and oxygen atoms in the compound.”

I need help to proceed.


texts:
Question:

Since the acetyl group provides $-M$, methyl $+I$ and chlorine $-I$, it is obvious that the correct order is as given in option $(a)$
However while solving such questions I would compare the inductive effect as well as resonance effect. Thats where I wondered what could be the inductive effect acetyl group has to offer


texts: pKa explanation through empirical formula?

texts: Suppose two compounds with, say, $\mathrm{p}K_{\mathrm{a}1}=2.8$ and $\mathrm{p}K_{\mathrm{a}2}=3.2$, and formulae $\ce{C_{$a$}H_{$b$}O_{$c$}}=\ce{C_{$p$}O_{$q$}(OH)_{$r$}}$ and $\ce{C_{$d$}H_{$e$}O_{$f$}}=\ce{C_{$u$}O_{$v$}(OH)_{$w$}}$, respectively, with given $abcdef$, $pqruvw$. Can we explain the above $\mathrm{p}K_\mathrm{a}$ with (ONLY) the knowledge of the given numbers of atoms of $\ce{C}$, $\ce{H}$ and $\ce{O}$ using the theory of Usanovich, and no knowledge of the internal chemical structure of the chemical bonds inside the two molecules?


texts: Why even the most volatile solvents leave a residue after evaporating?

texts:
After a solvent evaporates off of a surface there's always some residue left in the form of a strain.

Why it is the case even for highly volatile solvents such as acetone, toluene etc?


texts: How to convert Sodium Carbonate to Sodium Bicarbonate at home (CO2 scrubber)

texts:
Is it possible for me at home to react atmospheric $\ce{CO2}$ with sodium carbonate to make sodium bicarbonate.

I am seeing if I can take $\ce{CO2}$ out of the air.


texts:
Which oxygen atom is more nucleophilic in carboxylic acids?

If we look at this page, it says the carbonyl oxygen is more nucleophilic:

However, I also learned in class that $\mathrm{sp^3}$ atoms are more reactive than $\mathrm{sp^2}$ atoms.

So, in an $\mathrm{S_n1}$ reaction where the solvent is acetic acid, which oxygen attacks?


texts: What factors are important for quantitative analysis of a proton 1D-NMR spectrum?

texts:
Besides elucidating or verifying a chemical structure, NMR can also be used e.g. for quantifying a mixture of different chemicals.

Depending on the quality of the spectrum and the specific substance, integrating the NMR signals for the same molecule can result in significant variations from the actual ratio of nuclei, which is known from the chemical structure.

What factors do affect the quantification of NMR signals in a proton 1D spectrum? What precautions should one take during acquisition and processing of NMR spectra to make sure that the spectra can be analyzed quantitatively?


texts:
Gases are frequently described as "colorless, odorless, and tasteless."  I am wondering if this is redundant, since I can't think of many gases that have a detectable color to begin with, much less ones that have a color but no odor.

Are there any gases that are colorful and odorless at standard temperature and pressure?  In particular, gases that impart enough of a color to white light that one could look into a room filled with the gas and detect its presence visually?

(In the limit I suppose one could argue that a standard atmosphere is "colorful" since over many miles one can see blue scattering, but the question here is whether it is ever useful or helpful to describe a gas as "colorless.")


texts: Why does potassium form peroxides but sodium does not?

texts: As we go down the periodic table, Group 1 alkali metals hold their single outer valence electron more loosely, and so reactivity increases. Below potassium (Na, Li), we can store the metal in oil with no difficulty. Above potassium (Rb, Cs), we need to exclude all oxygen to prevent reaction in air. Potassium (K) is the unique element where we can technically store it in oil, but it is highly likely to react with any available oxygen to form explosive peroxides. I'd like an explanation of why this is; i.e. why is the reactivity favorable for the formation of peroxides. Thanks!


texts:
I know that there are polar uncharged amino acids (serine, threonine, asparagine, glutamine, cysteine) and polar charged amino acids (the basic and acidic amino acids).
Does the charge on the acidic and basic amino acids make them more polar and hydrophilic than the uncharged polar amino acids? Moreover, cysteine is classified as an uncharged amino acid, but because it has an ionizable side chain, would it be more polar than serine, asparagine, etc.?


texts: Is sodium "also known to turn purple and combust (like lithium)," when exposed to water?

texts:
I understand that indicator solutions can change color depending on pH, but the following statements in the Phys.org article Super cheap earth element to advance new battery tech to the industry has me baffled.

Most of today's batteries are made up of rare lithium mined from the mountains of South America. If the world depletes this source, then battery production could stagnate.
Sodium is a very cheap and earth-abundant alternative to using lithium-ion batteries that is also known to turn purple and combust if exposed to water—even just water in the air.

Later it says:

They minimized sodium's exposure to the moisture that would make it combust by making the sodium powder in a glovebox filled with the gas argon. To make the powder, they used an ultrasound—the same tool used for monitoring the development a fetus — to melt sodium chunks into a milky purple liquid. The liquid then cooled into a powder, and was suspended in a hexane solution to evenly disperse the powder particles.

Phys.org news items are generally of very high quality, so I'm wondering if this is just a mistake (perhaps a reference to the use of a pH indicator) or if there is some reaction between sodium, water and perhaps air that involves a purple color.
The "purple" statement is echoed on Purdue University's web page Super cheap earth element to advance new battery tech to the industry as well.
So far I've only found the video Sodium gas... omg it's purple!.
The paper in question is Ultrasound-assisted synthesis of sodium powder as electrode additive to improve cycling performance of sodium-ion batteries. Tang,  Kye and Pol, Journal of Power Sources, 396, pp 476-482, https://doi.org/10.1016/j.jpowsour.2018.06.067


texts: Why is dinitrogen tetraoxide less stable at high temperature?

texts:
I have calculated the enthalpy of dimerisation for the reaction at low temperature:

$$\ce{2NO2 <=> N2O4}$$
$$\Delta_\mathrm{dimerisation}\ce{H}= \pu{-13.87 kcal mol^{-1}}= \pu{-58.03  kJ mol^{-1}}$$

Also for this reaction, $\ce{\Delta S}$ is negative due to presence of more gaseous moles on LHS.

My book mentions that $\ce{N2O4}$ is stable only at low temperature. Why is it so? I couldn't find any reliable sources on the internet.


texts: How can I get ChemSketch to get N and H atoms closer while still operating in ACS style and without adjusting atom sizes?

texts: A person at wikipedia is getting on my case for creating this image because the N and H symbols are so separated even though this seems to be the default of ChemSketch (one of the softwares that's recommended for chem structure drawing in the Wikipedia manual of style) and I'd like to know how to make them happy and get the separation between the N and H shortened without changing the style and letter sizes.


texts: Delta G for Standard Hydrogen Electrode reaction

texts:
I’m dealing with electrochemistry problems.
For the following reaction
$$\ce{2H+ +2e- <=>H2}\quad E^\circ=0\ \mathrm{V}$$
Does it make sense to say
$$\Delta G^\circ=-nFE^\circ=0$$
Which would mean the reaction is in equilibrium?


texts: Why is the boiling point of heavy water more than that of normal water?

texts:
In class we learnt that the London forces become stronger as the relative molecular mass increases. Not just as in organic chemistry but in things like the halogens.

However, as I understand, the London forces are just temporary dipoles forming indicating that this would have nothing to do with the molecular mass but instead the number of electrons because there will be more electrons to form the dipole. This would mean that the trend would be stronger London Forces with more electrons instead of increasing molecular mass.

How can that explain the slightly higher boiling points of heavy water (deuterium oxide ~101˚C) than normal water?


texts: How do I create a concentrated solution of singlet oxygen (in the dark)?

texts:
Without appealing to reactions that require photons / light, how do chemists achieve a very high concentration of continually produced, though quite short lived, singlet oxygen in aqueous solution (i.e. $\ce{{}^1O_2}$ where dioxygen is typically in the triplet $\ce{{}^3O_2}$ state)?  I suppose I'll also ask the same question if we have the freedom to select an organic solvent of choice for the buffer?  By "high concentration" I mean at concentration from $\approx 10~\mathrm{\mu{}M} - 100(+)~\mathrm{\mu{}M}$.

My guess would be that should be a way to do this starting with a solution containing some amount of $\ce{H_2O_2}$, but I'm not quite sure what a reasonable process might be.

Here's the wikipedia link for singlet oxygen ($\ce{{}^3O_2}$)

This reaction should happen at or around room temperature.

The reason I'm specifying that I'd like to do this in the dark, and to have the singlet oxygen continually produced at room temperature (given its short lifetime, which is $\leq 100~\mathrm{\mu{}s}$ under any conditions I've heard of), is because I'm curious if I could easily set up some buffer that lets me dose a sample with singlet oxygen on a lab bench with a pipette.  Given the short lifetime of singlet oxygen, having to use a continuous radiation source presents difficulties that, while surmountable, lead me to ask this question.

Provided the above, I'd like to avoid reactions that vent gases like $\ce{Cl_2}$ and require fume hoods in the sense of "... well, if you value your life ..." vs. "... OSHA says so ...".


texts: Determining the stereochemistry of the product(s) when an alkyl shift in a carbocation generates a chiral carbon

texts:
Consider this carbocation:

We know that this carbocation would immediately rearrange - by a methyl shift - to form the more stable carbocation.

Now, notice that the migration will produce a chiral center at carbon 1. Assuming that the leaving group was a chloride, will the configuration at 1 - after the methyl shift - be retained, inverted, or racemized?

Interestingly, assuming the nucleophile is $\ce{EtOH}$, in the final product - 2-d-3-ethoxy-3-methylpentane, carbon 2 is also a chiral center. I assume that it will be racemized, as in usual SN1 reactions, but I am not sure. Am I correct?

At a very detailed level, I was also taught that in SN1 reactions, 100% racemization does not occur. The inverted product is slightly more than the retained product. This is because - while the leaving group is still leaving - backside attack is preferred. So, does this phenomenon also have an effect on the molecule above?

To conclude, I wish to know the stereochemistry at both chiral carbon 1 and 2. Are they retained, inverted, or racemized? If racemized, then is the racemization 100%, or is the inverted product formed more than the retained one?


texts: I would like to make some invisible ink that apears by itself after some time, preferably at least a couple of days. I want to write a dedication in a book with it, so it would probably be fine if the colour apears after half an hour of air exposure. Is this even possible using easy to get ingredients?


texts: Dissolving silver braze from tungsten carbide

texts:
I'm working out the best process to chemically strip silver brazing from tungsten carbide (WC) bits. My main objective is to recover the silver as a relatively pure metal. When I use $\ce{HNO3}$ at anywhere from 20-70%, it dissolves the solder and I end up with a red solution.  When I try to use cementation (putting copper metal in the solution) to precipitate the $\ce{Ag}$ as sponge, it isn't working.

Can any one help me figure out what's going on here?  The brazing being used should be 50-60% $\ce{Ag}$ by weight. I'm not sure yet if there is $\ce{Pd}$ or not.


texts: How does beta decay increases the stabilization of the nuclei?

texts:
How does beta emission by a nuclei increases the general stability of it? I surely am not a specialist or anything, but this just don't make sense to me, since the objective of radiation is to release energy, but I can't figure out exactly how it's done.

The loss of energy from the electron getting expelled, in addition to its kinetic energy, roughly gives half a MeV (source). Besides, as the strong force acts similarly on protons and neutrons, I guess it won't change considerably in piratical effects. Thus, in my conception, at least, the eletrostatic repulsion from the proton added should overlap the energy who got rid in the process.

Hence, I am confused. I wish to understand how it plays a role in nucleus stabilization.


texts: A compound that reacts with ethyl magnesium bromide and also decolorizes bromine water

texts:
Which of the following compounds reacts with ethyl magnesium bromide and also
decolorizes bromine water solution:

Is the answer only option (c)?


texts: What does this example mean? Slow cooling of 40% Sn alloy from 800°C to 600°C: L → L and γ → L, γ, and ε → L and ε

texts:
It's in a phase diagram topic. It's about $\ce{Cu}$-$\ce{Sn}$ phase diagram.

And it has a question of:

Write the schematic diagram describing the following scenarios and identifies the regions and the phases when Slow cooling of $13.1\%$ $\ce{Sn}$ alloy from $\pu{1000^\circ C}$ to $\pu{300^\circ C}$ happens.

I have this schematic diagram that describes the following scenarios and identifies the regions and the phases at $40 \%\,\ce{Sn}$ alloy from $\pu{800 °C}$ "$\ce{L -> L}$ and $\ce{γ -> L}$, γ, and $\ce{ε  -> L}$ and ε" as an example but it's confusing to follow. However, it's just an example and it doesn't follow the $\ce{Cu}-\ce{Sn}$ phase diagram anyway.
But does the first one mean $\ce{L -> L +  γ}$?
And L , y are in different phases that manages to fall both at $40 \%\,\ce{Sn}$ alloy from $\pu{800 °C}?
Also am I correct to assume that the final one means $\ce{ε -> L + ε}$?
This is the closest image that I can give based on my assumption:

Development of microstructure in eutectic alloys (II)
At compositions between the room temperature solubility limit and the maximum solid solubility at the eutectic temperature, $\beta$ phase nucleates as the $\alpha$ solid solubility is exceeded upon crossing the solvus line

[MSE 2009: Introduction to Materials Science; Chapter 9: Phase Diagrams; Page 28]

Here's the PDF file for more information.
"$\ce{L -> L}$ and $\ce{γ -> L}$, γ, and $\ce{ε  -> L}$ and ε" is a schematic diagram for the slow cooling which means it is an equilibrium cooling Like this image given below:

Equilibrium Cooling in a $\ce{Cu-Ni}$ Binary System
Phase Diagram: $\ce{Cu-Ni}$ System.
System is:
--binary: i.e 2 components: $\ce{Cu}$ and $\ce{Ni}$.
--isomorphous: i.e., complete solubility of one component in another; a phase field extends from $0$ to $100\,\mathrm{wt}\%$
Consider $C_o = 35\,\mathrm{wt\%}$ $\ce{Ni}$

Another one is:

Ex: Cooling of $\ce{Cu-Ni}$ Alloy
Phase diagram: $\ce{Cu-Ni}$ system
Consider microstructural changes that accompany the cooling of a $C_o = \pu{35 wt\%}\, \ce{Ni}$ alloy

Cored vs Equilibrium Structures
$C_o$ changes as we solidify

These images are from this PPT file.


texts:
Butyllithium isomers are all stored in alkane solvents. Theoretically, equilibrium should (given enough time) lead to formation of mostly n-hexyllithium in the case of  n-BuLi stored in (mostly) n-hexane, I believe. I understand that the kinetics of deprotonating an alkyl proton are extraordinarily slow, apparently even in the case of the much stronger t-BuLi in pentane (which isn't merely thermodynamically neutral; it should be thermodynamically favorable for the lithium to exchange with the proton of a less substituted carbon).

I was wondering, though, does anyone know of any instance where a significant portion (or any observable portion, really) of something like t-BuLi has been noted to have reacted with alkane solvents?

All searches I've attempted have given me completely unrelated results, and even attempting to sift through them, I have come away with no mention of the idea, even.

Also, would the addition of some kind of lithium-binding reagent such as TMEDA or 15-crown-5 increase or decrease the rate here (assuming no Brønsted reaction between BuLi and the ligand)?

I ask because BuLi will typically deprotonate a heteroatom before doing nucleophilic addition, but will do nucleophilic addition (to a carbonyl) before deprotonating most "softer" carbon acids, suggesting alkyllithiums are pretty hard bases. I'm assuming making a more "naked" carbanion would make a harder base (more charge-driven than "HOMO-LUMO overlap"-driven), and I'm wondering if that could make it slower to react with an alkyl proton (though, an unstabilized carbanion is a fairly hard nucleofuge, so I could see the reaction going faster, too).


texts: Grouping of symmetry classes in chemistry character tables

texts:
In the C3v point group, it lists three sigma Vs together in one column (class), and it doesn't list the  cVs separately. Consequently there are three irreducible representations.

In the C2v point group, however, it lists 2 separate cVs in separate columns. Consequently there are four irreducible representations.

My question is, why are the cVs grouped together in C3v, but not grouped together in C2v?


texts: Electrophilic Substitution with Ceric Ammonium Nitrate and Lithium Bromide as reagents

texts:
The 2020 IChO Preparatory Problem List (source here) had the following reaction as part of the solution to the first question:

(CAN = Ceric Ammonium Nitrate).
What is the mechanism for this 'Electrophilic Substitution' of the ring? I have not encountered such a reaction before. As far as I'm aware, CAN is an oxidizing agent, whereas Lithium Bromide would dissociate to give $\ce{Br-}$, which is not an electrophile. Aromatic Nucleophilic Substitution (ArSN) is out of the question here, as the ring is highly activated by the methoxy group.
The only probable reaction I can think of is that CAN successively oxidizes $\ce{Br-}$ to $\ce{Br2}$, then to $\ce{Br+}$, but this seems unlikely, and I could not find such a reaction mentioned anywhere in literature. A mechanism for this reaction, preferably along with a reference, would be much appreciated.


texts: is there any difference between glycerin and glycerol?

texts:
In laboratory setting, is there a difference between glycerin and glycerol?

There are some conflicting info on this topic.


texts: Aren't all semiconductors' atoms bond in a covalent bond? How is a "covalent semiconductor" different from other semiconductors?


texts: Redox Reaction Equation with elusive oxygen

texts:
I've been balancing redox equations for the last couple of weeks and have become quite accustomed to the procedure however I've come across an equation that eludes me every which way when it comes to balancing oxygen. I come to the next to last step to balancing my redox equation but am unable to write my net ionic equation.

  Liquid hydrazine reacts with an aqueous solution of sodium bromate. Nitrogen gas and bromide ions are formed.

I am asked to balance this reaction in an acidic solution.

I first write out my equation:

$$\ce{N2H4(l) + NaBrO3(aq) -> N2(g) + Br- (aq)}$$

I break my equation up into two half equations, one being my oxidant equation and the other my reductant. I balance them both:

$$\ce{N2H4(l) -> N2(g) + 4H+ (aq) + 4e-}$$

The other half of the equation is where I get stuck with balancing the oxygen. I end up balancing the hydrogen on both sides to be 10 but I come up short of one oxygen on my product side.

$$\ce{NaBrO3 (aq) -> Br- (aq)}$$

I use the algebraic method to assign an oxidation number to $\ce{Br}$ on reactant side of half equation.

$\ce{Br + Na + 3O = 0}$

$\ce{Br + 1 + 3(-2) = 0}$

$\ce{Br - 5 = 0}$

$\ce{Br = 5^{+}}$

$\ce{Br}$ on the product side has an oxidation number of -1 equal to its net charge

In order to balance the oxidation charge of both sides, I add $\ce{6e-}$ to the reactant side. This then brings the oxidation charge to -1 on both sides of the half reaction.

$$\ce{NaBrO3(aq) + 6e- -> Br- (aq)}$$

I then compensate net charge of the acidic reaction by adding 5 hydrogen ions to the reactant side to bring the net charge on both sides to 1-.

$$\ce{NaBrO3(aq) + 6e- + 5H+ (aq) -> Br- (aq)}$$

I then must add water to the product side in order to balance Hydrogen and oxygen atoms in the half reaction. I have 5 hydrogen for reactants so I must add 2.5 water molecules on the product side to match hydrogen.

$$\ce{NaBrO3(aq) + 6e- + 5H+(aq)->Br- (aq) + $2.5$H2O(l)}$$

Staying customary to the law of combining volumes and Avogadro's hypothesis I multiply the half equation by 2 to get a whole number for water

$$\ce{2NaBrO3(aq) + 12e- + 10H+(aq) -> 2Br- (aq) + 5H2O(l)}$$

The oxygen atoms here elude me. I can't figure out how to balance them. I figured I took a wrong turn on the way but my troubleshooting comes to no avail thus far. Can anyone fill me in on this little secret?


texts: I have a sample of gallium (a few grams). I've noticed every time I melt the gallium and refreeze it, it forms this grey skin on the outside. When I remelt the gallium, this portion doesn't melt and remains a dull grey color. I have skimmed it off every time and collected it. I looked it up and gallium doesn't seem to create an oxide or other compound unless under extreme conditions. I have noticed this when melting it in a plastic bag, a glass beaker, and a plastic container. I have been using hot water to melt it, but the water doesn't contact the gallium, only the container. It seems I am slowly losing gallium from my sample and have a small amount of this grey material saved in case it can be recovered. Does anyone know what this is and how it can be reverted to elemental gallium?


texts: Changes in entropy of the universe in a reversible reaction

texts:
Does entropy of the universe always increase in one of the forward or backward reactions of a reversible reaction and decrease in the other?

If no then how do you explain the entropy of the universe increasing in both directions or decreasing in both directions?!?

If yes, do we get more of the reaction that increases the entropy of the universe? I would presume yes as all real processes increase the entropy of the universe.


texts: Ionization energy and charge localization: π-bonds/systems and ionization energy

texts:
Page 35 of my textbook, Mass Spectrometry by Jürgen H. Gross, says the following in a section on ionization energy (IE) and charge localization:

  Molecules with π-bonds have lower IEs than those without, causing the IE of ethene to be lower than that of ethane. Again the IE is reduced further with increasing size of the alkene. Aromatic hydrocarbons can stabalize a single charge even better and expanding π-systems also help making ionization easier.

My questions are as follows:

Why do molecules with π-bonds have lower IEs than those without?
Why does expanding π-systems help making ionization easier?

I would greatly appreciate it if people could please take the time to clarify this.


texts: Why is arsenic trichloride more likely to be polar than aluminum trichloride?

texts: According to my chemistry teacher, $\ce{AsCl3}$ is more likely to be polar than $\ce{AlCl3}$. Why is this? As I understand it, the difference in electronegativity is what makes a compound more or less likely to be polar, and $\ce{AlCl3}$ has a much greater difference between the two elements' electronegativities. So why isn't it more likely to be polar of the two?


texts: Is the correct zeroth-order wave function $\phi^{(0)}$ an eigenfunction of the perturbation Hamiltonian $H'$?

texts:
Consider the perturbation treatment of He $1s2s$ excited state configuration. The quantum mechanical Hamiltonian for the He-atom is:
\begin{aligned}
\hat{H} = \sum_{i=1}^2 h_i + \frac 1 {r_{1 2}} \\
h_i = -\tfrac 12 \nabla_i^2 - \frac 1 r_i
\end{aligned}
In the following perturbation treatment, the unperturbed Hamiltonian $\hat{H}^0$ is $\sum_{i=1}^2 h_i$, while the perturbation Hamiltonian $\hat{H}'$ includes the inter-electron repulsion $r_{1 2}^{-1}$.
The four unperturbed degenerate wave functions $\psi^{(0)}$ are shown below as Slater determinants:
$$
\begin{aligned}
&\psi_1^{(0)} = \left|\begin{array}{} 1s(1) \overline{2s}(1) \\ 1s(2) \overline{2s}(2) \end{array}\right| \equiv \left| 1 \overline{2} \right\rangle & \psi_2^{(0)} = \left| \overline{1} 2 \right\rangle \\
&\psi_3^{(0)} = \left| 1 2 \right\rangle &\psi_4^{(0)} = \left| \overline{1} \overline{2} \right\rangle
\end{aligned}
$$
The correct zeroth-order wave functions $\phi^{(0)}$ for the perturbation Hamiltonian $\hat{H}'$ are linear combinations of unperturbed eigenfunctions such that $\phi^{(0)} = \sum_i c_i \psi_i^{(0)}$. Solving for $\phi^{(0)}$ using the linear variational method is equivalent to diagonalizing the perturbation Hamiltonian $\hat{H}'$ in a basis of $\psi^{(0)}$. The eigenvectors and eigenvalues of the $\mathbf{H}'$ matrix, whose elements are $\left\langle \psi_m^{(0)} \middle| \hat{H}' \middle| \psi_i^{(0)} \right\rangle$, are the correct zeroth-order wave functions and the corresponding first-order corrections to the energy, respectively.
Because $\left\langle \psi_{m \neq 3}^{(0)} \middle| \hat{H}' \middle| \psi_3^{(0)} \right\rangle = 0$ (the Condon-Slater rules), $\psi_3^{(0)} = \left| 1 2 \right\rangle$ is already the eigenvector of the perturbation Hamiltonian $\hat{H}'$ with the eigenvalue $E_3^{(1)} = \left\langle  1 2 \mid \mid 1 2 \right\rangle = \left\langle  1 2 \mid 1 2 \right\rangle - \left\langle  1 2 \mid 2 1 \right\rangle$. Could you suggest whether it is correct to go on to state the eigen-equation of $\hat{H}'\psi_3^{(0)} = E_3^{(1)} \psi_3^{(0)}$ ?


texts: Why is methyl α-D-glucopyranoside preferentially formed from glucopyranose in acidic methanol?

texts:
According to my textbook Organic Chemistry 2e by David Klein, the formation of a glycoside from glucopyranose favors the α form (see picture below).

Why does this happen? Shouldn't the equilibrium favor the β form, where the methoxy group is in an equatorial position and has less steric interactions?


texts:
If a reaction has positive $\Delta G$ then reverse reaction has negative $\Delta G$. How can both occur simultaneously, e.g., in a reversible reaction such as dimerisation of $\ce{NO2}$ to form $\ce{N2O4}$? Do forward and backward reactions occur spontaneously? How can both directions be spontaneous at the same time?
I read in some book that  Haber's process to form ammonia is spontaneous at a temperature below $170\ \mathrm{^\circ C}$ (the author proved this using $\Delta G=$ negative for spontaneous process). This means that above this temperature $\ce{N2}$ and $\ce{H2}$ shouldn't combine to form $\ce{NH3}$. But industrially Haber's process is performed at temperature around $400\ \mathrm{^\circ C}$. Isn't this a contradiction?


texts: Polystyrene properties after dissolved by acetone

texts:
Polystyrene plastic can be dissolved in acetone.
I would like to understand:

If the dissolved polystyrene will take-out of the acetone and becomes solid again (after all the acetone evaporates), will this solid polystyrene keep the same material properties as it was before the dissolving process?
How can I speed-up the solidification of the dissolved plastic?


texts: Why a particular enantiomer of a diastereomer shows affinity towards another?

texts:
A particular enantiomer can show affinity towards another enantiomer of another diasteromer eg. body receptors with chiral drugs, chiral stationary phase of chromatography etc.

But what's the reason behind this affinity? A broad answer will be encouraged.


texts: Can water be ignited in an ozone atmosphere?

texts:
According to my calculations, the reaction $\ce{H2O + O3 -> H2O2 + O2}$ should be favourable under standard conditions. However, I am told that the reaction is probably very slow in solution since ozone is poorly soluble in water and the reaction occurs through a radical mechanism.

Water can be ignited in a fluorine atmosphere. Can water also be ignited in an ozone atmosphere? Can this be done at 1 atm?


texts: Which isomers of C6H4(OH)2 has a higher melting point?why?

texts:
At first I thought that the first isomer must have the highest melting point since it's the most polarized isomer. So I looked them up on Pubchem to be sure and the answer was exactly the opposite;the third isomer has the highest melting point and it's not polar.

Any idea why?

Thanks!


texts: How do we know that we have isolated a substance?

texts:
In The Historical Background of Chemistry by Henry M. Leicester page 131, the author says:

  Carl Wilhelm Scheele (1742-1786) [...] isolated many organic compounds, including hydrogen cyanide, lactic, citric, and malic acids, and glycerol.

But how did Scheele know that those substances were isolated?

According to me, we can’t be sure of that without doing some very high-tech analyses.


texts: Why are silicon and germanium used as semiconductors but not other metalloids?

texts:
The semiconductor materials are either elementary such as silicon and germanium or compound such as gallium arsenide. Silicon is the most used semiconductor for discrete devices and integrated circuits.

However, other metalloids like antimony and tellurium are not used as semiconductors. Is it because they are too expensive to extract or is there another reason for this?


texts: SN2 reaction with alkyl bromide and pentanenitrile?

texts:
Is it possible to do a Friedel-Crafts alkylation on a plain alkane such as the one I've attached below, or is it only reserved for EArS mechanisms?
Also, I was wondering what would happen if I tried this reaction with another halogen on the starting substrate (if I had 1-bromoethane for example)...

Edit 1: I realize now that the top reaction doesn't make sense. Rather than a Friedel-Crafts Alkylation, I think I found a mechanism to make this type of reaction work (SN2) with Br as a leaving group and CN as a strong nucleophile, but I'm not sure...

Edit 2: I miscounted the carbons.

Edit 3: This is what I understand, from the suggestions given...


texts: Markovnikov's addition to halogenated alkene?

texts:
The justification or rather intuition behind Markovnikov's rule is the stability of intermediate carbocation. The more substituted the carbocation the more stable the product. But based on this ideas how can we satisfactorily explain the following reaction?
$$\ce{CH2=CHCl + HCl -> CH3-CHCl2}$$


texts:
In regard to the mechanism of halogen addition, consider the situation when we add a halogen (say, bromine) to an unsymmetrical alkene about the double bond (say, propene) in the presence of $\ce{CCl4}$.

I knew the mechanism would be something of this sort:

  A cyclic bromonium ion would be formed with the two carbons of the double bond. The second bromide ion (acting as a nucleophile) attacks on the more substitued carbon from the side opposite to the bromonium ion to cause ring opening and formation of a vic-dibromide.

My teacher however tells me that other than ethene, no other alkene forms bridges like these, because of unstability of bromonium complex due to repulsion between substituents on carbon and the bridged element.

I have two questions in this regard:

Which of the two is the correct mechanism?
If the former is indeed the correct mechanism, then would the nucleophile  attack the least substituted carbon? (seeing as how the partial positive charge on the more substituted carbon is nuetralised to a greater extent due to $+I$ effect of attached methyl/ethyl groups).


texts: Single electron reduction of ketone by Na or Zn

texts:
Whenever we add Na or Zn metal to a ketone, why does the electron prefer to attack the carbonyl bond and form a radical, instead of removing the acidic hydrogen and forming an enolate and $\ce{H2}$ gas?

I was thinking that usually when we add Na and there is a sufficiently acidic Hydrogen present, it reacts and releases $\ce{H2}$. I just wanted to know if there is an advantage in attacking the carbonyl bond instead of an acid-base reaction. Also, is this dependent on kinetic or thermodynamic control.


texts: Flow tests using safe acids and bases and an indicator

texts:
I want to conduct some visualization tests on a new mixing device.  I would like to mix acid with base and use an indicator to see a color change.  These are flow tests and the flow rates of acid and base will be equal.  I'd like to only use a stoichiometric excess of 20% of either the acid or base.

Since I will be conducting these experiments in my basement, I'm thinking I should probably try to use acids and bases that are safe to humans.  I suppose I could use a 0.001M concentration of HCL and NaOH.  But I'd be handling more concentrated solutions prior to dilution to these concentrations.

I could maybe use something like baking soda for the "base" and vinegar for the "acid".  Since these are weak, there will be equilibrium shifts during the reactions in order to use up all of either the acid or base (depending upon which reactant is the 20% excess).  I need the reaction to be very rapid such that the several microsecond mixing that I am expecting will be rate controlling.

Any suggestions for acids/bases and indicator that I might use?  A strongly colored indicator in the weak acid or base would be strongly preferred. It would be best if after reaction, that indicator was colorless or an opposite color prior to reaction (red or blue converting to yellow). Again, please note that the flowrate of acid will be identical to that of base (around 0.2 gpm) except that either the acid or base will have a molarity that is 20% higher than the other reactant.

Thanks.


texts: When it comes to bond energy or molecular binding energy, do people mean enthalpy?

texts:
When calculating bond energy or molecular binding energy, which value should I use, enthalpy or total energy?

For example, A+B=C

Should it be C's enthalpy of formation minus (A's+B's)enthalpies of formation,
or C's total energy minus (A's+B's) total energies?


texts: Dehydration of primary alcohols without a β-hydrogen

texts:
What happens in dehydrations of primary alcohols (in presence of acid catalyst at high temperatures) which don't have a β-hydrogen?

For example, in the case of neopentyl alcohol, will it dehydrate as it doesn't have a β-hydrogen? Obviously, E2 reaction will not be possible, but can it react via an E1 reaction, with a rearrangement in the carbocation step?


texts: In a single cell battery, is voltage exactly equal to cell potential?

texts: I've been researching electrochemical cells. In chemistry-focused sources, you usually see the potential difference between the electrodes referred to as cell potential, but in engineering/industrial sources(where you talk about "batteries") you usually see plain "voltage." Are the two always the same, or are there some situations where they're different(excluding multiple cells)? I want to know whether you can use the cell potential formula $$E^o_{cell} = E^o_{cathode} - E^o_{anode}$$ to calculate an accurate standard conditions voltage for a battery. If not, what gets in the way?


texts: Hand sanitizer is impossible to find around me and I have 4 family members who are essential and not around a sink or soap during their work day (delivery drivers), and they are out.  I make a lot of soap, shampoo, lotions, things like that and I thought hand sanitizer would be easy - but I was WRONG.  I have 99% anhydrous isopropyl alcohol and aloe vera gel.  Tonight I weighed everything to make it 70% IPA and 30% aloe vera gel.  It formed these solid squishy jelly clumps and didn't form a gel at all.  What am I doing wrong?  I added the IPA in kind of slow, but was stirring the whole time. I saw all these YT videos of people doing this and their gel/IPA combination makes a perfect gel.  HOW?!  I'm thinking about adding some HEC to help thicken it but am not sure to how it will react.  Ideas?


texts: Why are acetic acid and sodium bicarbonate mixed to unblock a drain?

texts:
I have always wondered about the rationale behind combining white vinegar and sodium bicarbonate to perform household cleaning jobs, and to unblock drains. I would have expected white vinegar to act well on its own as an acidic cleaner, and sodium bicarbonate to act well on its own as a base cleaner.
Does combining them not simply neutralise the potential of each to perform its job?
The same combination is often recommended for unblocking slow drains. Again, depending on what is blocking the drain, I would have expected that an acid or base would act well in isolation. And given that hair and soap are the likely culprits, I would have anticipated that sodium bicarbonate, a base, would be the more effective.
What is the justification for this? Is it, perhaps, the mechanical action of the carbon dioxide produced that is intended to lift whatever is blocking the drain? Or is there something else at play?
Thank you in advance.


texts: Possible side reactions in electrolysis of concentrated NaCl

texts:
This is a very basic question about which side reactions can take place if the electrodes are not shielded from each other during electrolysis of concentrated $\ce{NaCl}$.

So, this is the desired net reaction for this process:
$$2\ce{NaCl(l) + 2H2O -> 2NaOH(l) + H2(g) + Cl2(g)}$$

At the anode, oxidation of chloride ions to chlorine gas:
$$\ce{2Cl- -> Cl2 + 2e-}$$
At the cathode, reduction of water to form hydrogen gas and hydroxide ions:
$$\ce{2H2O + 2e- -> H2 + 2OH-}$$

The section 'The need to keep all the products separate' on this page gives $ 2$ by-products that are formed when $\ce{ H2}$ and $\ce{Cl2}$ stay in the system:
$$\ce{H2 + Cl2 -> 2HCl}$$
$$\ce{Cl2 + 2NaOH ->NaOCl + NaCl + H2}$$

I wonder if $ 2 $ additional side reactions can take place, simply with the gases diffusing to the other electrode, resulting in the reverse redox reactions:

At the cathode, reduction of chlorine gas to chloride ions:
$$\ce{Cl2 + 2e- -> 2Cl-}$$
At the anode, oxidation of hydrogen gas to form hydronium ions:
$$\ce{H2 + 2H2O -> 2H3O+ + 2e-}$$

Aren't these reverse (and spontaneous, based on the standard potential of these reactions) redox reactions also likely to happen when the electrodes aren't shielded?
Which one of all these side reactions (or maybe others?) are more likely to occur in this scenario? I think $\ce{ H2 + Cl2 -> 2HCl}$ as both are in gas form and are likely to encounter each other

Thanks a lot.


texts: Can the solutions for the Briggs Rauscher experiment be made ahead of time and stored?

texts:
I will be performing the Briggs Rauscher Oscillating reaction as a part of an investigation into the effect of heat on the antioxidants.

This will require 3 solutions to be mixed together, as shown below, to obtain a reaction which will oscillate between clear to yellow to a dark blue.

Solution A:
- 9%  $\ce{H2O2}$

Solution B:
- Acidified 0.2 M $\ce{KIO3}$ solution

Solution C:
- Solution of soluble starch/Malonic acid/$\ce{MnSO4}$

However, as I will be able to work on this in 45 minute blocks, I am unable to make up the solutions fresh every single time. Hence, I was wondering if it would be possible for me to make up enough solution at the beginning and store them for subsequent trials.

Does anyone know if these solutions can be made ahead of time and stored, without obviously affecting the reaction. If so, how for how long, and are any special conditions eg. refrigeration required?


texts:
I've seen that the first ionization energy of a particular metal is always greater than its work function. This implies that the valence electrons in an isolated atom are more strongly bound than the de-localized conduction electrons in the solid metal.

  For example, the first ionization energy of sodium is $5.14\mathrm {eV}$/atom.

  (source: here)

  while its work function is just $2.28 \mathrm {eV}$.

  (source: here)

I'm thinking that in a metal lattice, the de-localized electrons are attracted by many positive kernels at the same time. Also, they suffer repulsive forces from the electrons around. So the concerned electron is shielded from the attractive force from the positive centers  by the other nearby de-localized electrons and the the case isn't much different from that of an isolated atom. But that doesn't seem to be the case because the work function is (very roughly), just half the value of the ionization energy.

In metallic solids, after the formation of bands, are the de-localized electrons (which now exist in bands) attracted less strongly by the positive cores which gives rise to such a difference?

Is it the case always? If so, why?

Thank you very much for your valuable suggestions.


texts: Do hydrogen halides (HX) form strong or weak acids?

texts: I know that when dissolved in water, hydrogen halides ($\ce{H-X}$), become acids. I know that $\ce{HF}$ forms a weak acid, but can it be generalized that all $\ce{HX}$ acids do so?


texts: How to calculate the amount of gas in a compressed cylinder

texts:
I am trying to calculate a cost per hour use of a gas we buy in a cylinder. The details I have been working with are:

Gas used CP-grade N2 material number: 110628-L can

Gas: N, density = 1.251 g/L @ 0.101 MPa M (molar mas) = 14.007
Gas cylinder: Pressure = 200 bar or 20 MPa Cylinder volume 9.45 m3 or 9450 L
Operating pressure of gas from cylinder = 4.5 bar or 0.45 MPa and flow rate = 60 cL/min

I have been applying the ideal gas law to PV=nRT to figure out how many total litres of N are in the can at 4.5 bar pressure to then get a rough estimate of how many hours of flowing gas I get. However I seem to be getting unreasonable numbers, potentially from me using the equation or reasoning incorrectly:

When I apply the gas law under isothermal V2=V1/(P2/P1) conditions to see how much the internal gas volume expands from the 20 MPa pressure, as a sanity check I wanted to see how many L at 1 atm came out. The result was 1.89 ML which makes little sense as the conversion of 1.89 ML N2 to mass = 2.364 Mg.

Similarly it equates to 420 kL @ 0.42 MPa.

Where am I going wrong?

Maybe the specifications mean that its 9.45m3 or 9450 L of compressed gas to 200 bar?


texts: Why does the reaction quotient use the products (multiplications) of reactants and products, rather than their respective sums?

texts:
As you may know, the reaction quotient $Q_c$ is defined by the equation
$$
Q_c = \frac{[C]^\gamma [D]^\delta}{[A]^\alpha [B]^\beta}
$$
for the chemical reaction
$$
\alpha A + \beta B \rightarrow \gamma C + \delta D.
$$

This is something I've been struggling to understand at an intuitive level. Why is $Q_c$ the ratio of the product of the reaction's product concentrations and the product of the reaction's reactant concentrations (sorry for the confusing terminology; I can't think of a more precise way to phrase that), rather than the ratio of the sums of concentrations, like this:
$$
Q_c' = \frac{\gamma[C]+\delta[D]}{\alpha[A]+\beta[B]}
$$

This second, incorrect equation makes more sense to me because concentrations of solutes add up. Is the ratio defined as such so that it is directly proportional to the concentrations of each product and inversely proportional to the concentrations of each reactant? Is there some relation to kinetics that might give me a deeper insight into the meaning of this quotient?


texts:
Basic and acidic materials exist in nature, so it makes sense that our forefathers could know what happens when they react. I would like to know when and how did they learn about this. In particular:

a. What is the earliest time in which people could witness acid-base reaction that causes fire or explosion (as in this video)?  What are the earliest written accounts of such reactions?

b. What are the earliest written accounts of neutralization reactions?

c. When were acid-base reactions intentionally used, e.g. for neutralizations or to create explosions?


texts: Modelling pH as function of time and position

texts:
I already posted this on the Engineering Stack Exchange under Chemical Engineering as I don't know where it's a better fit.
I have a system whose initial state consists of three different sections with different chemical composition. All sections are aqueous solutions of different $\mathrm{pH}$ that are brought into contact for $t \gt 0$. The system is isothermal in each section and is of equal temperature in all sections and is assumed to remain isothermal, as heat generation is not considered. Section 1 (the leftmost section) is basic and contains reagent 1, section 2, the middle section, contains just water at a $\textrm{pH}$ of 7 and section 3, the rightmost section, is acidic. Section 1 and 3 are of equal size, whereas section 2 is larger. The system is three-dimensional, but can be reduced to one dimension due to symmetry (it is a tube in which angular and radial coordinates are assumed to not play a role). All sections can be considered equal in terms of physical properties (viscosity, density, etc.). I would like to model the $\mathrm{pH}$ as a function of time and position as there are reactions occurring whose reaction rate is a function of $\mathrm{pH}$. There is no convection, only diffusion. I already tried setting up a PDE system using
$$
\frac{\partial c_i}{\partial t}= D\nabla^2 c_i + r_i(\mathrm{pH},T)
$$
and solving it in Matlab, while setting a very high rate constant for the recombination of $\ce{H+}$ and $\ce{OH-}$. The Matlab solver fails as the recombination kinetics are too fast, but lowering them is not an option, as this wouldn't represent reality anymore (acid-base reactions are thought of the be instantaneous). How could I rewrite my PDE system to model the evolution of the $\mathrm{pH}$ at every position as well as calculate the concentrations of products and educts of reactions that depend on $\mathrm{pH}$ (but are only catalysed by it), without using reaction kinetics for the recombination of $\ce{H+}$ and $\ce{OH-}$ to make use of the fact that this reaction is instantaneous?


texts: Effect of pressure on transition temperature

texts:
I was wondering if someone can explain why the answer to the following question is volume instead of the others.

If pressure has no effect on the transition temperature between two
crystalline forms of matter the two forms have the same molar
(a) volume
(b) energy
(c) enthalpy
(d) entropy
(e) heat capacity

I know the answer is volume but I'm not sure which equation that comes from. I was thinking maybe the law of reduced properties but at this point I'm just guessing based on the answer and I know that that particular equation is for gases. Does anyone know if there's an analog for crystalline forms of matter or if there's a more intuitive explanation? Thanks!


texts: Why are d-d electronic transitions forbidden and weakly absorbing? Why do they occur at all?

texts: I am unable to understand why d-d electronic transitions are forbidden? Why are they weakly absorbing and apart from that, why do they occur at all?


texts: How would I name O-methylations on sugars while retaining the sugar’s common name?

texts:
Suppose I had a monosaccharide, e.g. D-arabinose. Suppose I do a few synthetic steps with it, and end up with the compound methyl (2S,3R,4R)-3,5-dihydroxy-2,4-dimethoxypentanoate. (as labelled by ChemDraw. If that is not the PIN, please correct.)

However, when writing my paper/thesis/lab report, I would love to derive the base name from D-arabinose for simplicity and consistency. The monosaccharide derivatives with a carboxylic acid in place of an aldehyde are -onic acids so my base name would be methyl D-arabinonate. But how would I correctly and unambiguously label the methoxy groups?

If I used 2,4-dimethyl, that would sound like this second compound:

And if I used 2,4-dimethoxy, wouldn’t that make it this one:

Is there a trick I am missing for clearly naming the compound as above with methyl D-arabinonate as a base name?


texts: Why does KMnO4 oxidize iodide to iodine in acidic medium, whereas iodide to iodate in alkaline medium?

texts: $\ce{KMnO4}$ should be a better oxidizing agent in acidic medium, than in alkaline medium, as per my knowledge. However, it oxidizes iodide (oxidation state = -1) to iodine (0) in acidic medium, whereas iodide (-1) to iodate (+5) in alkaline medium. The latter has a higher change in oxidation number, which we would have instead expected for the former. Why is this so?


texts: What is the reaction between diethyl malonate and hydrazine?

texts:
For the reaction of diethyl malonate with $\ce{NH2NH2}$ in aqueous medium in presence of $\ce{CH3CH2OH}$, I found two types of product with SciFinder:

In presence of $\ce{H2SO4}$, the reaction changes to:

$\ce{EtOH}$ is a good leaving group, but can you explain why there are two different types of products? With what mechanism can they be explained?


texts: Why do the d orbitals contract when pairing of electrons start, because the size should increase due to increase in energy

texts:
The energy of an orbital is proportional to its mean radial distance, and since the 3d orbital is much larger it is much higher in energy than the 3s and 3p orbitals

All references from JD Lee Concise inorganic chemistry

However, d orbitals are in general too large and too high in energy to mix completely with s and p orbitals.

In this caption, JD Lee says that the d orbitals find it hard to undergo hybridization because of its too large size and higher energy, but to decrease its energy and size , it employs various solutions, such as:

A second factor affecting the size of d orbitals is the number of d orbitals occupied by electrons. If only one 3d orbital is occupied on an S atom, the average radial distance is 2.46 A., but when two 3d orbitals are occupied the distance drops to 1.60 A.
A further small contraction of d orbitals may arise by coupling of the spins of electrons occupying different orbitals. It seems probable that d orbitals do participate in bonding in cases where d orbital contraction occurs.

One of them was that when electrons start filling in d orbitals, contraction of orbitals occurs. When pairing of electrons commences, d orbitals contract further.
But I find this line confusing, because the pairing/filling of electrons in the d orbitals must increase the energy, and thus the size, of d orbitals. But JD LEE states that the opposite happens. Could someone please explain why?


texts: How do we know the number of s and p orbitals in a shell?

texts:
How do we know how many s & p orbitals will be in a shell?

There is one 2s orbital and three 2p orbitals in shell #2.
There is one 3s orbital, three 3p orbitals and five 3d orbitals in
shell #3.

Is there a reason for this? Wouldn't four 2s orbitals for shell #2 be a configuration of lower energy?


texts:
While solving a question in organic chemistry, I needed to compare the strength of mesomeric effects of various groups.
I looked it up on Wikipedia, and it goes like this :

+M EFFECT ORDER :

–O− > –NH2 > –NHR > –OR > –NHCOR > –OCOR > –Ph > –F > –Cl > –Br > –I

-M EFFECT ORDER :

–NO2 > –CN > --S(=O)2−OH > –CHO > –C=O > –COOCOR > –COOR > –COOH > –CONH2 > –COO−

What is the way to understand such comparisons ? . Why does the -OH group show stronger mesomeric effect than the -NH2 group ? Also, why is an -OR group weaker than the -NH2 group ? Can somebody please explain ; I was unable to find a reasonable explanation through a google search.


texts: Which form of n-heterocyclic carbene is more basic and stable? ( Singlet or triplet)


texts: Are there any sulfides, sulfates, carbonates that cannot be dissolved by aqua regia?

texts: I was looking into these specific minerals: arsenopyrite, pyrite, chalcopyrite, barite, calcite, dolomite. I investigate issues with tellurides not showing expected gold concentrations.


texts: Does acetic acid give a positive result with the iodoform test?

texts:
Acetic acid contains a $\ce{-COMe}$ group, so theoretically, it should give a positive result in the iodoform test (i.e. a yellow precipitate of $\ce{CHI3}$ being formed).

But apparently the iodoform test is used to distinguish between acetic acid and other compounds with a $\ce{-COMe}$ group. So, logically, acetic acid must not give a positive result. Why is this so?


texts: Can amines in acidic medium last for long?

texts:
I have been thinking of a situation where amines are kept in moderately-to-highly acidic media. In such a case, the amines would assume the protonated forms:

$$\ce{RNH2 + H3O+ <=>> RNH3+ + H2O}$$

However, I don't think that the protonated amine would remain as it is. I feel that thermal agitations may cause the protonated amine to remove an ammonia molecule as a leaving group:

$$\ce{RNH3+ <=>[K] R+ + NH3}$$

The fact that a positively charged nitrogen is highly electron withdrawing, and might tug at the $\ce{C-N}$ $\sigma$-pair, seems to aid in the removal of an ammonia molecule, along with the fact that gaseous ammonia can easily remove itself from the medium, enhancing the reaction's equilibrium towards the forward direction. However the rather unstable carbocation that forms as a result of the deammoniation may prove to hinder this reaction, although the forming carbocation may be immediatly suppressed by the conjugate base of the acid used (like $\ce{Cl-}$, etc.) The overall reaction for an anime placed in conc.$\ce{HCl}$ could be:

$$\ce{RNH2 + HCl <=> RCl + NH3}$$

I have no lab equipments, nor the ability to access sources that confirm or reject my thoughts, so I decided to ask for help here. So, Can amines in an acidic medium remain as such for long periods, or release ammonia? If this doesn't happen at room temperatures, may this happen at a higher temperature?


texts: How to work out equations with period 3 oxides?

texts:
I know the general equation of reacting an acid with a base to be the salt and water, but I am not able to apply this to the following equations. So in what way can I derive the end product if I have never seen the reactants before?

For example, I can see the water is liberated out in the reaction between silicon dioxide and sodium hydroxide, producing this equation:
$$\ce{SiO2 + 2NaOH -> Na2SiO3 + H2O}.$$

However if the reactants were aluminium oxide and sodium hydroxide, how could I work out the equation:
$$\ce{Al2O3 + 2NaOH + 3H2O-> 2NaAl(OH)4}$$

I would have thought the product formed would be: $$\ce{Al2O3 + 3NaOH ->2Al(OH)3 + 2Na+}$$


texts: Equilibrium calculation gives negative molarity

texts:
There is a reaction: $$\ce {ClF3 <=> ClF + F2}$$ with $\ce {K_\mathrm{c} = 2.48 x 10^{-3}}$ Initially, $\ce {[ClF3] = 0.25 M} $, $\ce {[ClF] = 0.031 M} $, and $\ce {[F2] = 0.02 M} $. $\ce {F2}$ is added until the concentration of $\ce {F2} $ is $\ce {0.1 M} $.
  What is the concentration of these substances after equilibrium?

My attempt:
$\ce {ClF3 <=> ClF + F2} $

Initial concentration: $\ce {[ClF3] = 0.25 M} $, $\ce {[ClF] = 0.031 M} $, $\ce {[F2] = 0.1 M} $
Concentration that react: $\ce {[ClF3] = +x M} $, $\ce {[ClF] = -x M} $, $\ce {[F2] = -x M}$
Concentration after equilibrium: $\ce {[ClF3] = 0.25+x M} $, $\ce {[ClF] = 0.031-x M} $, $\ce {[F2] = 0.1-x M} $
So, $\ce {Kc = [ClF].[F2].[ClF3]^{-1}} $

I applied the concentration after equilibrium in $\ce {Kc} $, so I got:
$\ce {2.48.10^{-3} = [0.1-x].[0.031-x].[0.25+x]^{-1}} $

After calculate the equation above, I got $\ce {x = 0.1111 M}$.

Then my question is: if $\ce {x = 0.1111 M} $, so $\ce {[ClF] = -0.0801 M} $ and $\ce {[F2] = -0.0111 M} $. The concentration is negative. Is it possible? Are my steps incorrect or the answer is correct?


texts: Rate order of decomposition of hydrogen peroxide

texts:
I have been having some troubles finding a source for my investigation. I am inverstigating the decomposition of hydrogen peroxide, which (according to my teacher/supervisor) is a second order reaction with the use of catalase, and looks like this:

$$\ce{Rate = [H2O2][catalase]}$$
My investigation requires the rate order, but I am not supposed to calculate it myself due to "the high chance of errors in the experiment". I thought this wouldn't be an issue and was willing to investigate said rate equation myself, though it is not an option at my school and the teacher. I have been advised to find a source which states proves this, though I have been having hard time doing so myself.

Are there any articles or research papers I could purchase/read which would allow me to justify my statement for the previously mentioned rate order?


texts: Confusion regarding reaction pathway followed in reaction with lucas reagent

texts:
Recently I came across a problem involving Lucas reagent. It asks what is the major product when 2-methylbutanol is treated by HCl in presence of anhydrous ZnCl2? The answer says major product is 2-chloro-2-methylbutane. The reason it gives is 1,2 hydride shift. But my question is whether Sn1 reaction will even occur? I knew primary alcohols always follow Sn2 mechanism.Hence no rearrangement would take place.Can someone clarify what's happening?
Thank you


texts:
Here's an image:

The left side is designed to be fitted into a beaker, and it captures gas evolved during a reaction.  The right side can be filled with a liquid to then react with that gas.  We use it to capture ammonia from a decomposition reaction, with an indicator in the right half as part of an identification test.  I'm sure it must have a name, it's a commercial piece of glassware, but the box we keep it in in the lab doesn't identify it.


texts: Test for chlorine and chloramine in city water supply

texts:
I am looking to install a water filter system and I wanted to test the water for free and total chlorine.

I understand from the city water report that it uses chloramine and NO chlorine (test report)and that chloramine content averages around 4 ppm in the water supply. I purchased one of these to test it out. http://www.bulkreefsupply.com/insta-test-free-total-chlorine-strips-lamotte.html

The above product can measure free and total chlorine ( 0, 0.5, 1, 3, 5, 10 ) PPMs. I was surprised to find out after using these test strips that city supply has 0 PPM for both free and total chlorine.

Questions
1. Any idea how I can test if these test strips are indeed working?
2. Anything wrong with the way I have tested?


texts: How can the outermost electrons in silicon be 2s and 2p electrons?

texts:
My book says the number of outermost electrons in silicon is $4$. Yes, right. But then it says those are $\ce{2s}$ and $\ce{2p}$ electrons. The electronic configuration of silicon is $\ce{1s^2  2s^2  2p^6  3s^2  3p^2}$.

How are the outermost electrons $\ce{2s}$ and $\ce{2p}$ electrons. Those belong to third shell.

Then it says the maximum number of electrons in the outermost shell is $8$. Correct. But then it says those  are $\ce{2s + 6p}$ electrons. How?


texts: What are the gaseous outputs of electrolysis of Water along with NaOH or KOH?

texts:
Theoretically electrolysis of water yields Hydrogen and Oxygen in gaseous form.
But to enhance conductivity we have to add an electrolyte like $\ce{NaOH}$ or $\ce{KOH}$.
Does this produce any other gases along with Oxygen? Does $\ce{Na+}$ or $\ce{OH^-}$ ions also come out as some form of gas? Or practically speaking can people breathe the oxygen which comes out of electrolysis?
What are the gaseous outputs of electrolysis of Water along with $\ce{NaOH}$ or $\ce{KOH}$?


texts: How does the vapor pressure in a vessel affects the total pressure after a combustion reaction?

texts:
The problem is as follows:

  A sealed container of $3\,L$ in capactity is filled with hydrogen and
  oxygen at $314\,torr$ each one at a temperature of $27^{\circ}C$. A
  spark produces the reaction between oxygen and hydrogen. Find the
  total pressure after the reaction supposing that the temperature does
  not change. (You may use the vapor pressure of water at $27^{\circ}C$
  is $27\,torr$)

The alternatives given are:

$\begin{array}{ll}
1.&157\,torr\\
2.&184\,torr\\
3.&312\,torr\\
4.&468\,torr\\
5.&494\,torr\\
\end{array}$

What I've attempted to do to solve this problem was to establish the initial conditions for the reaction:

$$O_2+2H_2\rightarrow 2H_{2}O$$

The number of moles for each gas can be found as follows: (for the sake of brevity I'm omitting units)

$n_{O_{2}}=\frac{PV}{RT}=\frac{314\times 3}{62.4\times 300}= 0.0503$

$n_{H_{2}}=\frac{PV}{RT}=\frac{314\times 3}{62.4\times 300}= 0.0503$

Both gases have the same number of moles.

From the reaction I could spot that the limiting reagent in this case is the hydrogen thus it will the one to be used for the calculation of the amount of water produced.

Since both hydrogen and water are in the same proportion the moles of water will be the same as what are the hydrogen.

$n_{H_{2}O}=0.0503$

While for the amount of oxygen which will remain will be half of the value since:

$0.0503\,mol H_{2}\times\frac{1\,mol\,O_{2}}{2\,mol\,H_{2}}=0.0252\,mol\,O_{2}$

Therefore this will be established as follows:

$\begin{array}{llll}
O_2&2H_2&\rightarrow&2H_{2}O\\
1\,mol&2\,mol&&2\,mol\\
0.0503&0.0503&&0\\
-0.0252&-0.0503&&+0.0503\\\hline
-0.0251&-0.0503&&+0.0503\\
\end{array}$

From this I went on to calculate the pressure for each:

For the water:

$P=\frac{nRT}{V}=\frac{0.0503\times 62.4 \times 300}{3}= 313.82$

For oxygen:

$P=\frac{nRT}{V}=\frac{0.0251\times 62.4 \times 300}{3}= 156.62$

But since it was given that the vapor pressure of water is $27\,torr$ made me confused on how should I use this given information. Does it mean that should I subtract from the oxygen?.

If I do that I obtain:

$156.62-27=129.62$

Then I assumed that this pressure can be added to the pressure of water:

$313.82+129.62=443.44\,torr$

But using this is way off from any of the alternatives in the given answers:

But If I add all the numbers:

$313.82+156.62+27=497.44\,torr$

Which is seems close to one of the alternatives but the number swapped. $468\,torr$

I'm not certain if this is due significant figures or an error in the problem. The source of my major confusion is exactly how should it be assesed the information regarding vapor pressure in a combustion reaction?. I'm assuming that after the combustion the water vapor formed will excert a pressure in the container so does this must be added to the pressure of the water formed resulting from the moles produced?.

Can somebody help me with this and clear out my doubts?.


texts: What products come from the electrolysis of sodium bicarbonate?

texts:
I did an experiment finding the electrolysis of various solutions. One of them was sodium bicarbonate and tap water. I want to be able to scientifically explain my results, using chemical equations and explanations of those equations. Can somebody help?

-Thanks


texts: Testing for asbestos using readily available chemicals and tools?

texts:
Given that it is difficult to determine who is telling the truth in the recent claim that J&J covered up finding asbestos in their powder, is there any chemical test that we can perform on our own to determine with reasonable confidence whether the particular sample of powder we have bought contains asbestos? (I am aware that one test involves viewing the sample under a sufficiently high-powered polarizing light microscope, but not everyone has such a tool.)
I have not much chemistry background beyond high-school, and it seems that there are numerous kinds of asbestos, apparently characterized more by their large aspect ratio than by their chemical composition. For example, chrysotile (which accounts for ≈95% of asbestos in buildings in the US) has an idealized chemical formula $\ce{Mg3(Si2O5)(OH)4}$, but may not even occur as exactly that. Talc according to wikipedia is either $\ce{H2Mg3(SiO3)4}$ or $\ce{Mg3Si4O10(OH)2}$. These break down as follows:

Chrysotile: $\ce{(Mg^2+)3[Si2O5]^2−([OH]^−)4}$
Talc A: $\ce{(H+)2(Mg^2+)3([SiO3]^2+)4}$
Talc B: $\ce{(Mg^2+)3[Si4O10]^4−([OH]^−)2}$

So we cannot test for $\ce{Mg^2+}$ or $\ce{[OH]^−}$. But is there a chemical test for $\ce{[Si2O5]^2−}$ that can be done at home? And is it safe to rule out chrysotile if no $\ce{[Si2O5]^2−}$ can be detected, or can the amount be too low for chemical detection but still dangerous?


texts:
Here I need to give the systematic name of this molecule so I decided to first find the longuest chain of carbons which seems to be the one I put in red. Then I have 2 ethyls at 3 and 4 and I have an isobutyl at 6 so would the name be

3,4-diethyl-6-isobutyldecane ?


texts: Bad repeatability of GC-FID meassurements

texts:
I am new to GC-FID and I am struggling with calibration curve. And I am strugling with the repeatability of measurements. One vial measured 5× in a row provides results which differs even 2 orders of magnitude. Do you see any mistakes in my procedure below?
I need to be able to quantify about 12 substances, mostly glycoles. I use methanol as solvent. I determined their retention times and prepared a calibration solution of these substances. All of them were clearly recognisable from each other in the chromatogram.
Since I need to quantify the substances, I prepared 10 solutions of the calibration substances. I need my results in % (m/m), therefore my calibration series was 10 g of solution + 10 g of methanol, 9 g of solution + 11 g of methanol, 8 g of solution + 12 g of methanol, … , 1 g of solution + 19 g of methanol. I mixed every one of them and fill the vials to the brim. I used only unused septa, put the vials in the refridgerator sealed with parafilm until they are measured.
Every sample was measured 5× in a row and the consequent measurements differed even 2 orders of magnitude. There was no trend in the signal intensity. I am not used to such a behaviour in spectroscopy measurements.
Do you see any mistakes in my procedure? Is there an error in method parametres settings?
Thank you for any help.


texts: Theory of volume contraction in solution

texts:
When a solid is dissolved into a liquid, or two solids are amalgamated, their mutual volume will contract. For example, a crystal of sugar having a volume of one cubic inch dissolved into 10 cubic inches of water will have less than 11 cubic inches of volume.

Is there any theory that explains exactly the degree of contraction, and can correctly predict the contraction for any given solute and solvent?


texts: How well will molten iron chrysolite (fayalite) react with hydrogen?

texts:
The equation balances nicely, but would the reaction tend to proceed this way? What temperature and time would be needed?

$\ce{Fe2SiO4 + 2H2 -> 2H2O + 2Fe + SiO2}$

There is no problem with supplying the energy to maintain a molten mix under the envisioned scenario, even up to pretty high temperatures. It's a solar furnace on the Moon. It can be left to boil as long as there is sunlight, which in some polar locations would actually be for months, elsewhere for 2 weeks at a time.

I have been trying to narrow the questions I ask here down as I seek an approach to bulk glass production in an advanced lunar colony. In consideration of that, it is important to bear in mind that the entire process is at high temperature and there is no exposure to the atmosphere, other than the gases that come from the mix - the furnace is outside, in the hard vacuum. The steam is pumped off and condensed, and if it is advantageous to maintain low pressure the pumping can achieve that.


texts: Why is the rate of a reaction proportional to the concentrations of reactants raised to their stoichiometric coefficients?

texts:
Consider a gaseous state elementary reaction $$\ce{aA(g) + bB(g)} \overset{k_\mathrm{f}}{\underset{k_{\mathrm{b}}}{\ce{<=>}}}\ce{ cC(g) + dD(g)}$$

I know that for this reaction, $$\Delta G = \Delta G^{\circ} + RT \ln \left( \frac{P_{\mathrm{C}}^c P_{\mathrm{D}}^d}{P_{\mathrm{A}}^a P_{\mathrm{B}}^b} \right) \tag1$$

Now, if $$K = \left( \frac{P_{\mathrm{C}}^c P_{\mathrm{D}}^d}{P_{\mathrm{A}}^a P_{\mathrm{B}}^b} \right) ,$$

then $\Delta G = \Delta G^{\circ} + RT \ln K$.

Now, how can we say that $$K = \frac{k_{\mathrm{b}}}{k_{\mathrm{f}}}$$

and $r_\mathrm{f} = k_{\mathrm{f}} \cdot P_{\mathrm{A}}^a \cdot P_{\mathrm{B}}^b \,$  and $\, r_\mathrm{b} = k_{\mathrm{f}} \cdot P_{\mathrm{C}}^c \cdot P_{\mathrm{D}}^d$
$\,$where $r_{\mathrm{f}}$ and $r_{\mathrm{b}}$ are rates of forward and backward reaction as assumed in this answer.

I want that to know that how can one prove rigorously that $r_\mathrm{f} = k_{\mathrm{f}} \cdot P_{\mathrm{A}}^a \cdot P_{\mathrm{B}}^b \,$  and $\, r_\mathrm{b} = k_{\mathrm{b}} \cdot P_{\mathrm{C}}^c \cdot P_{\mathrm{D}}^d$.


texts: Can a product be alcohol free while containing isopropyl myristate or isopropyl palmitate?

texts: I always find isopropyl myristate and isopropyl palmitate in cosmetics, and I want to know if they have alcohol in them or not. I read that they are composed of alcohol and acid, but they are considered to be conditioning agents, so does that mean that there is no alcohol left in them? So can a finished product be alcohol free while containing isopropyl myristate or isopropyl palmitate?


texts: Why isn't hydration an oxidation reaction?

texts:
http://chemistry2.csudh.edu/rpendarvis/OxRed.html  states,

  Addition or removal of water does not involve, by itself, an oxidation or a reduction reaction. The addition of water to an aldehyde to form a hydrate does not involve oxidation or reduction.

But in this reaction,

The oxidation states of the carbons change from

-3, -1 to -2, -2

As the oxidation states have changes, shouldn't it be considered a redox reaction?

  An oxidation-reduction reaction is any chemical reaction in which the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron Source


texts:
In the preparation of $\ce{Ag}$ doped $\ce{ZnO}$ thin films by sol-gel method, I dissolved zinc acetate in 2-propanol while adding DEA and the solution is ready.

After that I added different concentrations of $\ce{AgNO3}$ to the solution, stirring on a stirrer, starting with $0.005$ concentration, but I found that it didn't completely dissolved even after $20$ minutes, and it gets harder for higher concentrations. Can I get any help for this?


texts:
I have to examine the exact material of a specific fabric (non-woven), of which I know is either viscose or cotton. I know that viscose and cotton are structurally similar, but there should be a way to tell them apart.

This is the result of the microscopic examination (x 100):

My professor tells me this is viscose, but I thought of cotton because of the long fibers. But I also know that cotton has a 'twisted' look under the microscope.

My professor doesn't give any more clues, which leaves me with a bit of a problem. How can I tell the two apart? Does the picture show enough evidence for viscose (because of the linear structure)? I would like to double check this, just to be sure.


texts: Will glycerol and citric acid react? If yes, under what conditions?

texts: I would like to know whether the reaction will take place if glycerol and citric acid are merged? In particular, what will happen if both substances are heated up to high temperature (+100°C)?


texts: Why is the chemical formula for ethanoic acid CH3COOH and not C2H4O2?

texts: Why does the hydrogen ion move to the front of the formula and not to the subscript of the H already in the formula?


texts: Difference between base-promoted and base-catalysed

texts:
Why is halogenation of ketones in base described as being "base-promoted" and not "base-catalysed"?

If the reaction is not "catalyzed" then how is the base used up?


texts: Solute and Solvent classification in a Solution

texts:
When I look up the definition of solute and solvent, the definition by the Oxford English Dictionary is
solute

/ˈsɒljuːt,sɒˈljuːt/

noun

the ***minor*** component in a solution, dissolved in the solvent.

What does minor imply here? Does it classify them as solute and solvent as per mass/volume comparison? Or does it refer to their concentration?


texts: Nomenclature of organic compounds containing complex side chains

texts:
How do we decide the sequence of substituents in a organic compound if one of the substituents is complex. Should the complex chain must always be written first while writing the IUPAC name or are there any other rules governing it?

The following IUPAC names got me confused:

7-(1,2-dimethylpentyl)-5-ethyltridecane

AND

5,5-dimethyl-6-(1,1-dimethylbutyl)-6-pentyltridecane

In the first compound the complex substituent is written first although p(pentyl) comes after e(ethyl).

In the second compound, the complex substituent is written later although m(methyl) comes after b(butyl).


texts: What solvent would have the fewest ions?

texts:
We know that water auto-ionizes (to a rather small extent).

My question is which solvent would have the fewest ions (or at least fewer ions than water).

I'm thinking that perhaps some kind of hydrocarbon, as these are both weaker acids and weaker bases than water and thus even less reactive. I've seen computers submerged in oils (as well as distilled water) due to their low conductivities.


texts: Yesterday I made a mixture of vinegar and salt and then electrolyzed it. I was just wondering if anyone could tell me what the process created. For instance, would it create ethane?


texts: How to control the purity and quality of fatty acids or their CoA thioesters?

texts:
Background: We are looking into getting a series of cis-mono-unsaturated very-long-chain (C20-C32) fatty acids (with different, specific double-bond positions) — and/or the corresponding acyl-Coenzyme A thioesters — synthesised by a company. These compounds are to be used in primary research for a biochemical enzyme activity assay.

Question: Would MS or 1H-NMR be preferable for quality control/identification of such (custom-synthesised) compounds? Or would it not matter for these compounds at hand? What would be the advantages/disadvantages of these two options we are being offered?


texts: Azeotropes and separation by distillation?

texts:
I have just recently learnt the theory of fractional and normal distillations and the basics of maximum and minimum boiling azeotropes.

Most books say that the components of the mixture forming an azeotrope cannot be separated by distillation because on heating, the residue (in case of negative or maximum boiling azeotropes) and the distillate (in case of positive or minimum boiling azeotropes) is closer in composition to the azeotropic composition and always approaches it.

This being understood, we at least separate one component from the mixture as the residue (for positive azeotropes) and the distillate(for negative azeotropes) is richer in one component than the other since the remaining part approaches the azeotropic concentration thereby increasing the concentration of one of the components depending on which side of the azeotropic "point" are we on the graph of boiling temperature and composition.

If this is true, for any mixture, we can at least theoretically obtain one purified component (provided we have enough quantities of the mixture)??
Reference azeotrope basic


texts:
I have read hat there is two types of electric fields exist in galvanic cell.I understand E because of charges accumulated on electrodes but what about other E -field? What does cause this field and what is the direction? Detailed answer with explanation in terms of ions and charge will be helpful.

Full thought and Reasoning : In a galvanic cell when we immerse electrodes in solution,both electrode get charged.This building of charges is the result of chemical reactions on both sides. Now we in this process of building charges on the electrode if we see individual electrode ,lets say on one electrode there is negative charge (-ve) is building due to chemical reaction.This reaction also result in extra metal ions in solution which will be equilibrium with the electrode in joining the it and again separating with it again. Now I have understood till now .I know that there will be electric field between electrode due to these charges built  on electrodes.My question is what about the ions in the solution of negative electrode(-ve ) side  and lack of ions on the positive electrode side ? Will there be any Electric field from Positive to Negative electrode due to these ions (there are in different solution & different beakers )?
Example : Let's say We have a circuit containing battery and a resistor.In that circuit

In above image what is fs  . it is adding to E which means it has to be some kind of Electric field.From where did it come ? That's only my question .Thank you


texts:
It is given voltaic cell
  $\ce{Cu}|\ce{CuSO4}(\pu{10^-3 M})||\ce{CH3COONa}(10^{-2})|\ce{Pt}(\ce{H2})(\pu{1 atm})$.  Find the potential at $\pu{50^\circ C}$.
  Given $K_\mathrm{a}$ for $H= 1.8 \times 10^{-3}$.
  $E_{\ce{Cu^2+/Cu}} = \pu{0.336 V}$

When voltaic cell starts working: $\ce{H2}$ becomes $\ce{2H+}$. In the other hand $\ce{CH3COO-}$ hydrolizes forming $\ce{CH3COOH}$ and $\ce{OH-}$. We know $K_\mathrm{a}$ and we can find $K_\mathrm{b}$. And from that we can find the concentration of $\ce{OH-}$ and after that using the formula $\mathrm{pH}=14-\mathrm{pOH}$  we can find the concentration of $\ce{H+}$.

Now how we can find the concentration of $\ce{Cu^2+}$ in order to replace it into Nernst equation?
\begin{align}
  E &=E^\circ - \frac{RT}{nF} \cdot \ln\{\text{Qc}\}
  \text{, where}&
  \text{Qc} &= \frac{[\ce{H+}]}{[\ce{Cu^2+}]}.
\end{align}


texts: The effect of concentration on the rate of a homogenous reaction

texts:
I have to do an experiment where I will find out what the influence of the concentration on the rate of a homogenous reaction is.
We are asked to create 2 solutions, respectively A and B:
$$\ce{KI + Na2S2O3 + Starch + water}$$
and
$$\ce{H2O2 + H2SO4 + water}$$
As long as A and B aren't added together, the reaction cannot start.
Now what I'm supposed to do is make 10 different A and B solutions and add these together and measure the time it takes for the solution to turn blue (Iodine + Starch as an indicator).

Now, my problem is that the following questions are also asked:
"Write down the different reactions that take place"
This seems dubious to me but might not be.
e.g. Does dissolving into ions also count as a reaction?
Does the Starch (for which I have no given chemical formula) react in solution A?
I've also read online that adding $\ce{H2O2}$ and $\ce{H2SO4}$ creates a "Piranha" solution ($\ce{H3O+ + HSO4- + O}$ or $\ce{H2SO5 + H2O}$, I've found both online but I don't know which is correct here.)
In conclusion I just don't know which reactions I should give (Everything that happens in A and B isolated from eachother or everything that happens when I add A and B together? Either way, I'm also not sure what the reactions would be because, for instance, I don't have any certainty on what the chemical composition of the Starch is.)
Is the reaction a multistep reaction or a single step reaction? Why? If it's a multistep reaction, write down the partial reactions
Assuming that adding B to A is "The" reaction, how do I find out if there are multiple steps or not? How do I find these steps?
Given that this question is asked already makes me think that it is in fact a multi-step reaction.


texts:
I have 2 statements , and i am not sure, whether they are true or false.

Proteins like albumin and haemoglobin are insoluble in water

(in my view , almost all proteins are soluble- so this is a wrong  statement)

Proteins which are soluble in water have complex 3D structure and they are globular molecules. - (in my view I think this is also wrong)

Please explain these statements.


texts: I've been using this drug SID 347829124 - PubChem in my experiments from a vendor that supplied it as a $\ce{. 2HCl}$ version, and I switched to another supplier that has a free base instead. The two compounds have different solubility  in water and it would be desirable for me to obtain the $\ce{. 2HCl}$ form to avoid using $20\%$ dimethylformamide to solubilize the free base powder. I thought that using water with a stochiometric quantity of $\ce{HCl}$ would do the trick, but if somebody from the community could confirm this it would be very helpful.


texts:
Suppose I fill a vacuum chamber with 99% oxygen, then pull a vacuum on it down to 10 pascal absolute. If I then vaporize aluminum (for vapor deposition), will the aluminum bind with the remaining oxygen and create say a 0.1 pascal vacuum?

I'm not a chemist or a physicist, but it seems logical that the heavier (and high melting point) aluminum oxide molecules would collect on the walls and floor of the container resulting in a high vacuum mainly containing vaporized aluminum.

I am looking to experiment with aluminum vapor deposition and want to avoid buying a diffusion or turbo molecular pump. Seems like this should work, but I have not found any documentation on it. I'm not looking for optics quality here, so maybe high vacuum is not an issue in the first place.

Let me know if you guys think I should post this on the Physics SE instead. Thanks!


texts: Is the reaction between powdered soap and water exothermic?

texts: I have done a fair share of hand washing using powdered soaps and in the first few seconds after mixing the soap with water, I have in most cases felt a subtle warmth in my hands. Is it that the reaction (if there's any) between soap and water is exothermic? Or there is another  explanation for this phenomenon?


texts:
A solid piece of sulfur has a characteristic smell.

Is the smell of solid sulfur the result of the release of compounds like sulfur dioxide or hydrogen sulfide from a reaction with air or moisture, or is it from elemental sulfur particles that are being released by sublimation?

If it is from pure Sulfur particles (at least in part), what form is it released into the air, ie $\ce{S8}$ or $\ce{S2}$ or something else?


texts: Drying sodium tetraborate for use as a standard

texts:
I am currently attempting to purify technical grade sodium tetraborate decahydrate by recrystallization for use as a titration standard. I don't have a requirement for a specific grade or purity. I'm just looking to improve my results a bit.

I understand that one of its qualities for use as a primary standard is the stable hydration number. However, if I'm drying wet crystals, what would be the best way to ensure that there is no extra water without affecting this? Could heating produce the pentahydrate or anhydrous form?

This is a separate question really, but would it be better to convert to boric acid, recrystallise and then neutralise with a sodium base?


texts: Weight Percent of Solutions Given Without Units

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I have been performing haloform reactions using sodium hypochlorite. The most available source is common household bleach, which is a solution of $\ce{NaClO}$ in water. The bottles invariably give a concentration in unitless percentages: e.g., "$6\%$ Bleach."

I have assumed this to mean: (mass of solute) / (mass of solution) * 100.

Now I see that there are other (mathematically erroneous) uses of the percent symbol %, including a measure called WV (weight volume), which seems to be normalized by dividing gram weights of solute by 100 ml.

An easy question, impossible without the units:

How many grams of $\ce{NaClO}$ are in one litre of $6\%$ household bleach?


texts: Is ΔS of a system related to temperature and change in enthalpy?

texts:
I often see the equation $\Delta S_\text{universe}$ = $\Delta S_\text{surroundings}$ + $\Delta S_\text{system}$, where $\Delta S_\text{surroundings}$ can be re-expressed in terms of the enthalpy change of the system as

$$\Delta S_\text{surroundings} = \dfrac{-\Delta H_\text{system}}{T}$$.

This leaves me wondering why $\Delta S_\text{system}$ cannot also be re-expressed (or at least is never written) as a term with some combination of $\Delta H$ and $T$ (Maybe as $$\Delta S_\text{system} \overset{?}{=} \frac{- \Delta H_\text{surroundings}}{T}$$ although this would make $\Delta S_\text{universe}$ equal $0$).

Instead, $\Delta S_\text{system}$ is usually given as a standard value, seemingly independent of temperature. Is there a reason why we can only express the change in entropy of the surroundings, but not the change in entropy of the system, as related to the change in enthalpy and the temperature of a reaction?


texts:
Classical bioisosteres are functional groups that satisfy with the Grimm's hydride displacement law and Langmuir's definition of isosteres.

My question is why chlorine can be replaced by trifluoromethyl or cyano group and the replacement is categorized in univalent atoms replacement?

Because as seen from the criteria of classical bioisosteres aforementioned, the replacement atoms do not have any hydrogen atom therefore I think Grimm's law is devoid. However both trifluoromethyl and cyano group do not have the same number of atom nor electron as well as electron arrangement as in chlorine.

So what explains that these functional groups are classical bioisosteres?


texts: What chemical could be used as carbon monoxide scrubber?

texts:
I am trying to produce nitrogen by passing air over a heated tube of coals. This leaves a mixture of $\ce{CO},$ $\ce{H2O}$ and $\ce{N2}.$ Only $\ce{CO}$ is unwanted in this case.
Could I use calcium hydroxide to scrub carbon monoxide out of the gas? What other substances could be effective?
edit: this is part of challenge to make other chemicals from natural resources, therefore i have to obtain nitrogen myself instead of buying it


texts: How much water evaporates in a vacuum before freezing?

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I placed a container with 1000 grams (1 kg) of water at room temperature (20 degrees Celsius) inside a vacuum at 0.03 atm pressure. The water boiled for a few seconds then froze solid.
I need to calculate how much water evaporated before freezing occurred. Anyone know a formula I could use?


texts: How does molecular orbital overlap affect energy?

texts: If there is more overlap of the same sign wave function, this apparently leads to lower energy. I don't understand why. My professor said that there would be fewer nodes, and fewer nodes means lower energy. However, why would overlap in general cause the energy to decrease?


texts: Does a messier room actually have higher entropy?

texts: When my chemistry teacher was explaining entropy, she used the analogy of a clean vs. messy room. What I'm wondering is whether a messy room really does have higher entropy. Does this still work on a larger scale? If not, can I trust the analogy?


texts: Test for glyphosate in water, boolean style

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Testing for contamination of the ever so popular glyphosate based herbicide "Roundup" in water is a service that many labs provide, one of them is the Microbe Inotec Laboratory . They use an enzyme to check for levels of of contamination in ppb, which, I'm sure, is rather a complicated process.

My question is, is there any way to test for it more easily, without finding the actual amount of glyphosate but only checking whether it's present or not?


texts: Why can't helium be solidified at 'ordinary' pressures?

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According to the UC Davis ChemWiki Chemistry of Helium, helium has a comparatively unusual property, specifically:

  Helium is the only element that cannot be solidified by lowering the temperature at ordinary pressures.

'Ordinary' referring to standard air pressure (1 atmosphere).  In order to solidify, there needs to be a corresponding pressure increase, with a projected density of:

  $0.187 \pm 0.009~\mathrm{g~mL^{-1}}$ at $0~\mathrm{K}$ and $25~\mathrm{bar}$.

So why can't helium be solidified at 'ordinary' pressures?


texts: Effect of H-bonding on o-nitrobenzoic acid

texts: My argument here is regarding the acidity of o-nitrobenzoic acid being greater than p,m-nitrobenzoic acid. In o-nitrobenzoic acid, there is an intramolecular hydrogen bond which makes the bond stronger and resists the release of H+ ion. Also going by that along with ortho effect in check shouldn't acidity of o-nitrobenzoic acid be relatively lesser? To what extent does hydrogen bonding affect the acidity?